[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
This fix PHPCS warning you can change `parent::` to `AbstractElementCollection::`. The result would be the same (yes, this looks like a static method call, but in fact it will call method of that class on this object).