Improved the sturdyness of repository deletion

[Joaquimmnetto]

Description

Refactoring of the extension, changing from a inheritance based structure, to a composition based one. This helps a lot with testing, and makes the code easier to understand, and it didn't changed any public interfaces, so it is entirely retro compatible.

The main points of the refactor are:

• Repository creation behavior isolated in the RepositoryFactory class
• The GithubRepository/SharedGithubRepository/GithubRepositoryFeature interceptors now inherits directly from AbstractMethodInterceptor.
• The underlying operations on Field-based interceptors are now in the RepositoryFieldOperations which is a slightly-changed, and has similar methods to the old GithubRepositoryFieldInterceptor.
• The slightly more complex object creation process is isolated in static factory methods in the interceptors.

Besides there were several some in the deletion code to make it more sturdy, the main ones being:

• deletions now are retried in case of non FileNotFoundException exceptions, and also checks if the repository still exists before trying deletion
• Catch blocks that ignored Exception exceptions in the deletion process, now are only ignoring FileNotFoundException (404) exceptions, to make more clear which errors are happening.
• Added tests for the specific situation of creating new repositories with the same name of existing ones.

The refactoring is isolated in the refactor/interceptors branch, for ease of comparison, and if so wished, a new PR with only the refactored code can be open as well.

Changes

• refactor of the interceptors structure
• sturdier deletion process

[Larusso]

I really like the new setup of the code!