Adds MUSIC XML -> PyNN interface generation factories for convering
XML specification to MUSIC proxy device ports.

Also adds CLE interface components to replace standard PyNNControlAdapter,
PyNNCommunicationAdapter, and BrainLoader to make use of the proxy factories.
These components will be referenced and loaded in the backend without having
to directly modify the CLE.

Change-Id: Ia8208cc3517332b0f6a517ffaaf4bb72a5402ff6