Xamarin Android fixes

Fixes:
* Flicking back and forth from the home and favourites view caused multiple favourite activities on the back stack.
* Favourites list is updated when displayed.
* Changes to .gitignore to localize Xamarin framework.
* Retrieve application context for a given context, to stop leaks.
* Search text input trimmed.
* Load more list row shows highlighted state.
* Layouts optimized.

Still to do on Xamarin Android:
* Image caching (generating bindings for this is a #nightmare#!)
* Handle ambiguous locations