Build the spritefont and XML files and add the compiled files to the package

[RonenNess]

To simplify the installation process.
If people wish to change the themes they should just download the XMLs / spritefont sources and edit them instead of making it editable by default which requires them to install fonts and set dll reference to Content manager.

[DavidFidge]

PR #139 makes this redundant, the build should always work now by building from ttf files directly rather than relying on installed fonts.