Minor repository refactoring

[AlexandraRoatis]

Description

1. moved AbstractContractDetails to modAionImpl
2. removed the AbstractRepositoryCache and moved all functionality to AionRepositoryCache

Type of change

Insert x into the following checkboxes to confirm (eg. [x]):

• Bug fix.
• New feature.
• Enhancement.
• Unit test.
• Breaking change (a fix or feature that causes existing functionality to not work as expected).
• Requires documentation update.

Testing

Please describe the tests you used to validate this pull request. Provide any relevant details for test configurations as well as any instructions to reproduce these results.

• existing tests

Verification

Insert x into the following checkboxes to confirm (eg. [x]):

• I have self-reviewed my own code and conformed to the style guidelines of this project.
• New and existing tests pass locally with my changes.
• I have added tests for my fix or feature.
• I have made appropriate changes to the corresponding documentation.
• My code generates no new warnings.
• Any dependent changes have been made.

[AionJayT]

LGTM