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
I think we would like to ship this dll with installer as Test infrastructure APIs, so we should use AssemblyVersionSharedInfo.cs as it's done in other projects, so that this dll is also versioned as product version.