ClientProvider improvements

Client Provider feature has been improved:

* `clientprovider-api` bundle created containing only interfaces. This bundle solves Maven dependency cycle issues.
* `test-helpers` module improved in order to offer factories and common helpers to be used in unit tests.
* Expand `AbstractProviderFactory` including common code of `ClientProviderFactory` and `APIProviderFactory`.
* Created unit tests of `clientprovider` module.