Mgcb update

* Updated all samples to use the new MG Content Builder tool

**Note, from this point you need to install the latest MG MSI installer to install the MGCB tool, which can be located from the Development Builds section at:
http://www.monogame.net/downloads/

Current Known Issues :
* SpaceWar is unable to process the XACT file
* iOS build complains about the EXIT() function - says it is no longer used
* Linux build fails to package the WMA file - Song processor content builder fail?