Improvements on Client/API Provider

Some improvements on Client/API Provider:

* Add `ProviderNotFoundException` and throw it provider factories methods. Adapters updated to throw this exception instead of returning `null` when there is no such provider. Update some tests too.
* Scan for implemented super-interfaces when trying to match generic types in `AbstractProviderFactory`. This solves a bug using CXF providers.
* Minor bugs solved in test application`ClientApplication`.