[TASK] Add MediaTypes to the Utility (Revision 4)

This changes Scripts/updatemediatypes.php so that it can include any custom MediaTypes
that we decided to register.

To register a custom MediaType, modify Resources/Private/AdditionalMediaTypes and run
the updatemediatypes script.

Change-Id: Ic74b618e518197096c4f6afc8066c8ed5e63e7f0
Revision-Id: a550667dabdf26e96e0d58da0491fe29662bb7c0