Add JobInfo hierarcy and related classes

[mziccard]

This PR adds model classes for jobs and related entities:

• Abstract JobInfo with subclasses: CopyJobInfo, ExtractJobInfo, LoadJobInfo and QueryJobInfo one for each type of job
• JobStatus and BigQueryError to represent the job's status (and possible errors)
• JobStatistics with subclasses ExtractStatistics, LoadStatistics and QueryStatistics

Unit tests are added for each class.

[mziccard]

Thanks @ajkannan for the comments I fixed all of them (hope so:)) in place.

[aozarov]

I am still going over the code, will ping you when done.
In the mean time if you want to cleanup the following check-style warnings:

Starting audit...
src/test/java/com/google/gcloud/bigquery/ExtractJobInfoTest.java:43:35: warning: Name 'WRITE_DISPOSITION' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/LoadJobInfoTest.java:49:35: warning: Name 'WRITE_DISPOSITION' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/TableInfoTest.java:101:44: warning: Name 'USER_DEFINED_FUNCTIONS' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:29: warning: Wrong order for com.google.gcloud.bigquery.JobInfo.WriteDisposition import. Use /google/src/head/depot/google3/tools/java/sort_java_imports.py to automatically sort your imports.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:75:35: warning: Name 'WRITE_DISPOSITION' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:76:27: warning: Name 'PRIORTIY' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:77:26: warning: Name 'ALLOW_LARGE_RESULTS' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:78:26: warning: Name 'USE_QUERY_CACHE' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:79:26: warning: Name 'FLATTEN_RESULTS' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:80:44: warning: Name 'USER_DEFINED_FUNCTIONS' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/QueryJobInfoTest.java:93:31: warning: Name 'QUERY_JOB' must match pattern '^[a-z][a-zA-Z0-9]*_?$'.
src/test/java/com/google/gcloud/bigquery/BigQueryErrorTest.java:5: warning: Wrong order for org.junit.Assert.assertEquals import. Use /google/src/head/depot/google3/tools/java/sort_java_imports.py to automatically sort your imports.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:51: warning: Wrong order for com.google.gcloud.spi.BigQueryRpc.Option.MAX_RESULTS import. Use /google/src/head/depot/google3/tools/java/sort_java_imports.py to automatically sort your imports.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:106:12: error: 'catch' is not followed by whitespace.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:127: error: Line is longer than 100 characters (found 101).
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:191:12: error: 'catch' is not followed by whitespace.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:289:63: error: '?' should be on a new line.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:306:12: error: 'catch' is not followed by whitespace.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:388:63: error: '?' should be on a new line.
src/main/java/com/google/gcloud/spi/DefaultBigQueryRpc.java:392:12: error: 'catch' is not followed by whitespace.
src/main/java/com/google/gcloud/bigquery/Acl.java:64:3: error: Modifiers out of order specified by style guide (http://go/java-style#s4.8.7-modifiers). Expected order: 'public abstract static'
src/main/java/com/google/gcloud/bigquery/QueryJobInfo.java:59: error: Line is longer than 100 characters (found 101).
src/main/java/com/google/gcloud/bigquery/JobInfo.java:64:3: error: Modifiers out of order specified by style guide (http://go/java-style#s4.8.7-modifiers). Expected order: 'public abstract static'
src/main/java/com/google/gcloud/bigquery/BaseTableInfo.java:168:3: error: Modifiers out of order specified by style guide (http://go/java-style#s4.8.7-modifiers). Expected order: 'public abstract static'
src/main/java/com/google/gcloud/bigquery/UserDefinedFunction.java:16: error: Line is longer than 100 characters (found 101).
src/main/java/com/google/gcloud/bigquery/BigQueryOptions.java:21:8: error: Unused import: com.google.gcloud.spi.DefaultBigQueryRpc. Use /google/src/head/depot/google3/tools/java/remove_unused_imports.py to automatically remove unused imports.
src/main/java/com/google/gcloud/bigquery/BigQueryOptions.java:22: warning: Wrong order for com.google.gcloud.spi.BigQueryRpc import. Use /google/src/head/depot/google3/tools/java/sort_java_imports.py to automatically sort your imports.
src/main/java/com/google/gcloud/bigquery/Schema.java:99:81: error: ':' should be on a new line.
src/main/java/com/google/gcloud/bigquery/Field.java:35: error: Line is longer than 100 characters (found 101).
src/main/java/com/google/gcloud/bigquery/ViewInfo.java:79: error: Line is longer than 100 characters (found 101).
src/main/java/com/google/gcloud/bigquery/ViewInfo.java:90: error: Line is longer than 100 characters (found 101).
Audit done.