Starting to add the new finder method in Association
Using th edefault finder method in Association
Adding some doc blocks
Renamed option in CounterCache from finderType to finder
Using Association::find() in Association::attachTo()

This allows us to use defined custom finders even for joinable associations.
Removed unit tests that were hard to follow and were fragile, the code
they covered is also covered by a few integration tests.
Adding a test case for using a custom finder for associations
Fix failing test.
Merge pull request #4342 from cakephp/3.0-association-custom-finder

3.0 association custom finder