[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
I bet we don't need this anymore because `getIterator` is returning new iterator instance each time. If that is so, then you can also inline the `$iterator` variable itself. Then also repeat same for all other places where `->rewind()` is used.

Be sure to add a test anyway that verifies that for collection proxies with multiple elements inside we have iterator at 0 index right after `getObject` call.