[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
Tricky if. Before the code required 1 annotation of BEMAnnotation type. Now the requirement changed to any annotation and if it's of BEMAnnotation type, then we'll process it. I guess this was made due mistake.

Maybe method like `assertAnnotationClass` defined in the `DefaultElementLocator` can be used in all locator classes to verify that each element of a given array is of required class.