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.