[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
As I said before, any `AbstractProxy` descendants can deal with `[]` in `@var` annotations out of the box. No need to write `is_array` and other magic use collection proxies. Just replace `\\QATools\\QATools\\PageObject\\Element\\IWebElement[]` with `\\QATools\\QATools\\PageObject\\Element\\WebElementCollection`.