Merge pull request #1 from XForms/master

Merge from Master
#19 Added missing WP ImageButton and Work in Progress (WIP) version of iOS ImageButton.

Also fixed some reference problems for the packages in the Windows Phone sample project and added full binding support of the ImageButton.
Merge pull request #20 from Bowman74/master

#19 Added missing WP ImageButton and Work in Progress (WIP) version of iOS ImageButton