Precompile TabPage before usage
Wrap pull down menu of TabPage behind an asynchronous loader

Pull down menu is fades in when once it is created.
Drop radial gradient from TabItem

Use image and color overlay instead
Add add animations for history and favorite delegates (fade)

This also adds needed properties for vertical scroll decorators
once they are created.
Move text field behind an asynchronous loader

Loader of the TextField is activated only once when the status of
the TabPage changes to active.
Set all models (favorites, history, tabs) as late as possible

An empty state is added before "historyList" and "favoriteList" states
to block entering into those states. Once a real state is entered for
the first time models are set respectively.
Add busy indicator for the tab page

Busy indicator is visible while page is not yet active
Merge pull request #112 from rainemak/tabPagePerf

[sailfish-browser] Decrease tab page loading time