Added Build Scripts for Windows

I don't know if this will be any help and get merged but, mostly I checkout the monogame develop branch have to rebuild all targets by hand regularly. So I created this batch file that can build all of them together.

* Added build script for windows platform, that can build WindowsDX, WindowsGL, Windows8, Android and WindowsPhone targets.
* Also added build-macos.sh and build-linux.sh but they are just placeholders atm.