* We had to move to the final API:
* Items -> TabItems
* Items.VectorChanged -> TabItemsChanged
* TabClose -> TabCloseRequested
* TabViewItem.Icon -> TabViewItem.IconSource
* TabRowControl has been converted to a ContentPresenter, which
simplifies its logic a little bit.
* TerminalPage now differentiates MUX and WUX a little better
* Because of the change from Icon to IconSource in TabViewItem,
Utils::GetColoredIcon needed to be augmented to support MUX IconSources.
It was still necessary to use for WUX, so it's been templatized.
* I moved us from WUX SplitButton to MUX SplitButton and brought the
style in line with the one typically provided by TabView.
* Some of our local controls have had their backgrounds removed so
they're more amenable to being placed on other surfaces.
* I'm suppressing the TabView's padding.
* I removed a number of apparently dead methods from App.
* I've simplified the dragbar's sizing logic and eventing.
* The winmd harvester needed to be taught to not try to copy winmds for
framework packages.
* We now only initialize the terminal once we know the size
Closes#1896.
Closes#444.
Closes#857.
Closes#771.
Closes#760.
