Validation errors refactor

[p1c2u]

Fixes #246

• All validation exceptions are subclasses of ValidationError
• All schema validation exceptions are subclass of ValidateError
• All request validation exceptions are subclass of RequestError
• All response validation exceptions are subclass of ResponseError
• ParameterError exceptions have name and location values.
• HeaderError exceptions have name value.

Backward compatibilities:

• Schema unmarshalling/validation returns Invalid* exception (InvalidData, InvalidParameter, InvalidRequestBody, InvalidHeader). Use __cause__ property to get root cause exception.
• InvalidSecurity exception renamed to SecurityNotFound

[codecov]

Codecov Report

Merging #473 (02590a4) into master (dcc431c) will increase coverage by 0.11%.
The diff coverage is 93.97%.

@@            Coverage Diff             @@
##           master     #473      +/-   ##
==========================================
+ Coverage   92.19%   92.31%   +0.11%     
==========================================
  Files         103      105       +2     
  Lines        2856     2939      +83     
  Branches      243      249       +6     
==========================================
+ Hits         2633     2713      +80     
- Misses        182      185       +3     
  Partials       41       41              

Impacted Files	Coverage Δ
openapi_core/validation/exceptions.py	87.50% <50.00%> (-6.95%)	⬇️
openapi_core/security/providers.py	82.35% <60.00%> (ø)
openapi_core/validation/request/exceptions.py	88.00% <87.87%> (-3.31%)	⬇️
openapi_core/validation/response/exceptions.py	92.85% <88.88%> (-0.48%)	⬇️
openapi_core/validation/request/validators.py	88.58% <96.66%> (+0.90%)	⬆️
openapi_core/contrib/django/handlers.py	100.00% <100.00%> (ø)
openapi_core/contrib/falcon/handlers.py	100.00% <100.00%> (ø)
openapi_core/contrib/flask/handlers.py	100.00% <100.00%> (ø)
openapi_core/security/exceptions.py	100.00% <100.00%> (ø)
openapi_core/templating/security/exceptions.py	100.00% <100.00%> (ø)
... and 4 more

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