Better database copy handling #57

Currently a workflow can fail during the copying of the live database into a versioned materialized database. This will lead to partially copied databases which use up free space.

There should be a way to check for the current amount of free space and calculate an estimated space requirement for the new db before launching the copy operation and report the error if there is not enough space.

In addtion, if there is a failure during the workflow operations, a custom error handling tasks should cleanup the partially created database and trigger a message indicating why it failed.