Various Updates to get the Content Pipleine working on Mac

Slight changes to the API to allow custom Loggers to be assigned,
This is useful for the Addins and any custom UI.
Changed the ContentTypeWriter to emit XNA style assembly
references for backward compatability (for now)
Updated the SpriteFont processor to attempt to write
compressed textures
Added Core.Graphics support for the FontHelper (thanks kjpou1)

Sorry about the line endings/tabbing not sure what is going on there.