Magn 5402 cont

After the separation of SystemTestBase into SystemTestServices, there were a number of additional cleanup steps required to remove unused references from projects. Additionally, the changes in this PR consolidate test base classes to make it easier for third party libaries to make tests of their code. 

In general, when writing tests for your Dynamo libraries, you should now be able to subclass one of the following:

GeometricTestBase - For unit tests that can use the geometry library.
SystemTestBase - For system tests that start Dynamo and can use .dyn files.
RevitNodeTestBase - For unit tests, runnable on Revit through RTF.
RevitSystemTestBase - For system tests, runnable on Revit through RTF.

PTAL:
- [ ] @jnealb (So you can get an idea of the restructuring of our test base classes)
- [ ] @pboyer

Merge:
- [ ] Revit2015