[WIP] Support multiple @find-by annotations

Still open tasks but basic support for multiple ```@find-by```. Still requiring some new unit tests and ```ElementCollection``` see #48 for more details.

Closes #13
Normal collections end up with 0 elements. But using a proxy or collection proxy will execute a locate of the elements if using count or any other function on the proxy.

In this case we will never have 0 for a proxy. Thats why I made it more generic, but maybe some minor refactoring or configuration is required.