Merge pull request #10 from cwensley/corlissdev

Big Wpf updates
Make the default Drawable constructor use non-multithreaded semantics, consistent with desktop platforms.
Make Drawable inherit from Container + implementation for Windows, Mac and Wpf. A stub implementation for Gtk.
Make Drawable inherit from Container + implementation for iOS.
Make Drawable inherit from Container: Fix for Winforms PixelLayoutHandler.
Make Drawable inherit from Container: Turn on WS_EX_COMPOSITED
Remove WS_EX_COMPOSITED flag that was added in the previous checkin.
Tab control test: added Add Tab button.
Winforms clipboard: extend logic for retrieving images.
WinForms: Fix Graphics.DrawImage() when drawing a portion of an image (source/dest was reversed)
Mac: Scrollable should set DrawsBackground so background color is visible when set
Mac: More resilient when adding/clearing items from a ToolBar
Fix obsolete Bitmap.FromResource (Assembly, string)
Add properties to Generator to more easily determine if it is a particular platform
Mac: More bounds checks for split panel positions (e.g. if height or width is zero)
Mac: Better handling of XamMac ImageMenuItem.Image property when it is null
Mac: Fix drawing directly on a view (translate needs to be based on window content size, not control size)
Mac: Save/Restore state per operation
Removed some unused code
Wpf: Report Control.Size properly
Wpf: Button should allow for mnemonic
Wpf: Fix Graphics.DrawImage when drawing a portion of an image at various scales