Feature/platform manager

Pushing the base code for platform-manager based on http://www.int6.org/development/monogame/easy-multi-platform-managment-with-monogame/

* Updated the copyright text.
* Added platforms; windows, metro, wp7, wp8, linux, macos, ios, android. Only windows is tested.
* Fixed XNA & GL projects.
* Updated namespaces.
* Updated build script names.