List.GetItemAtIndex now accepts negative indices
added List.InsertItemAtIndex
added List.ReplaceItemAtIndex
negative indices all around
new list tests for negative indices and new funcs
Delete missing class diagram.
NuGet Updates
Move TestExtensions to SystemTestServices
Make GeometricTestBase setup method virtual.

This also consolidates the methods marked at [Setup] for
RevitNodeTestBase so we can guarantee the setup order.
Add change to proj file for TestServices move,
Ensure DynamoCorePath is set in SystemTestBase
Cleanup unused references.

After the refactor of system test base, and the movement of
TestExtensions, many test libraries had unused references.
Revert image export to SetOfViews
Add system test.
Add unit tests.
Small name change of system test.
Merge pull request #3142 from Steell/negative-index

Negative indices for list nodes, and list insertion and replacement: MAGN-4816
Merge pull request #3232 from DynamoDS/MAGN-5509

MAGN-5509 View.ExportAsImage only exports current view
Merge pull request #3229 from DynamoDS/MAGN-5402-Cont

Magn 5402 cont
Merge remote-tracking branch 'origin/master' into Revit2015