Changes done for GEB-310 - Support navigating to page instances in addition to classes

Following changes were done:

- Extracted Interfaces for all the support classes.
- Added Uninitialized support implementations for the said interfaces
- Added PageInstanceNotInitializedException class.
Actually let's not do it. We should allow users to reuse the same page instance if they want to. We are able to reliably reinitialise a page.