Added Default-568h.png file

This file is included in the C# project templates but missing in the F#
ones. It allows to automatically resize the app window to fill the
iPhone 5 screen.
Updated iOS template files for Default-568h.png

iOS and Universal projects now include the Default-568h@2x.png file in
the Resources folder.
Merge pull request #628 from fabiogaragiola/master

Added Default-568h.png file and fixed iOS templates