[Refactoring] Extracted functions
Worked through login process
Adjusted callback of updateCategories()
[sailfish] Renamed CategoryModel in rootWindow
[sailfish] Renamed FeedItemModel in rootWindow
[sailfish] Renamed FeedModel in rootWindow
Added more function documentation
Adjusted callback of updateFeeds()
Adjusted callback of updateFeedItems()
Adjusted callback of catchUp()
Documented subscribe()