Allowing associations in Query::contain to specify a custom finder

This allows changing the finder method an associated Table uses for contains. Also, `/ORM/Association/SelectableAssociationTrait` was passing in "all" at all times to the Query, even if you changed the finder. This addresses #4408.

Thanks!
Instead of `_` prefixing variables, generally it is better to come up with better names. Given that arrays are pass by value you do not need to `_` type or options at all.