Improvements and refactoring (towards #62)

Station search results were converted into QAbstractListModel. As a consequence, #30 is fixed. I wasn't able to reproduce #66, as well, so I assume it's fixed too.

A downfall of this change is that saved Favorites will be lost: currently, saved list of favorites contains only station names, but we need station IDs to perform search. Also, selected stations and favorites are now saved per backend: ID is backend specific, so it doesn't make sense to save favorites globally anymore.

I quickly tested all backends and nothing seems broken. But I would suggest more extensive testing to be sure everything still works.

Also, due to the extent of changes, Ubuntu UI is definitely broken now. I only updated Harmattan, Symbian and BlackBerry 10 UI (as I have devices to test on).

PS: There are still some things related to station search results which can be cleaned up/optimized (like getting rid of StationsResultItem and StationsResultList in favor of Station and StationsList in parsers).