Add support to get all registered mesh types from the registrar.

Now you can get all the mesh types as a set, so you can easily check what
types are supported.

Change-Id: Ie0c9b9f9cfe7dcb0387cbc4bdfb83e661096e70f
Update documentation of the meshtypes id space.

Change-Id: I2ed4da9461bc2b84b2fbb3d09c31eb0ee62de1b6
Merge branch 'meshtype_id_space'

Change-Id: Ic1659f115792a32c1912eb9f0b0530df129ee6b0