MAGN-5402 Separate system test base into its own library.

This PR separates the base class for system tests into the SystemTestServices library. It then wires this library to a new sample library called SampleLibraryTests. The SampleLibraryTests library will then become the basis for a NuGet package DynamoVisualProgramming.Tests (http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5404).

After these changes, our core UI tests run, and our Revit system tests run, both of which use this refactored base class.

PTAL:
- [ ] @lukechurch 

Requires Merge:

- [ ] Revit2015
We need to say what this is actually testing. E.g. if an exception gets thrown, does it fail?

Can we provide an example of how to do readback tests to ensure that the output is correct?

I.e. I'd this sample to be fleshed out at just a little bit more