Use the NuGet WinRT DatePicker package for the Xaml platform.

The control is wired up, but is not currently visible [TODO].
Merge remote-tracking branch 'picoe/develop' into dev3
Xaml: fixes for font tests. Add placeholder conversion of SystemFont to fonts. This is something that will need to be done carefully for Xaml, as there are extensive guidelines.
Unit test fixes. Eto.Test has no associated UI, so unit tests must run without assuming the existence of an Application instance or particular widget implementations.
Remove obsolete IGraphicsCreate - related code.
Remove #if DESKTOP in Window and TreeView.
Test app: use feature detection rather than #if DESKTOP when creating a menu.
Remove #if DESKTOP in Application.
Remove #if DESKTOP from Window.cs.

Add testability hook to translate resource names in TestIcon.cs.
Fix typo.
Fix #189: iOS: Bug in BitmapHandler.DrawImage(graphics, source, destination). This fix uses a single code path for scaled and unscaled images, and uses clipping to ensure that only the relevant portion is rendered.
Improve BitmapSection.DrawImageToRect() test.
Uncomment a line that was accidentally checked in commented.
Merge commit 'f81c4927c0e1a7434d95cb4295c9907027479fe7' into develop

* commit 'f81c4927c0e1a7434d95cb4295c9907027479fe7':
  Uncomment a line that was accidentally checked in commented.
  Improve BitmapSection.DrawImageToRect() test.
  Fix #189: iOS: Bug in BitmapHandler.DrawImage(graphics, source, destination). This fix uses a single code path for scaled and unscaled images, and uses clipping to ensure that only the relevant portion is rendered.
  Fix typo.
  Remove #if DESKTOP from Window.cs.
  Remove #if DESKTOP in Application.
  Test app: use feature detection rather than #if DESKTOP when creating a menu.
  Remove #if DESKTOP in Window and TreeView.
  Remove obsolete IGraphicsCreate - related code.
  Unit test fixes. Eto.Test has no associated UI, so unit tests must run without assuming the existence of an Application instance or particular widget implementations.
  Xaml: fixes for font tests. Add placeholder conversion of SystemFont to fonts. This is something that will need to be done carefully for Xaml, as there are extensive guidelines.
  Use the NuGet WinRT DatePicker package for the Xaml platform.

Conflicts:
	Source/Eto - Xaml.sln
	Source/Eto.Platform.iOS/Forms/IosWindow.cs
	Source/Eto.Test/Eto.Test/TestIcons.cs