Fix MAGN-3093 select node (Select Model Element) to show in "error state" when nothing is selected
UpdateManager configuration

- Implemented UpdateManagerConfiguration class to store the
configuration data specific to UpdateManager
- This class can be serialized and de-serialized into/from xml file.
- UpdateManager initializes the configuration from
UpdateManagerConfig.xml file if present in Dynamo installation,
otherwise by default it will point to production servers for
UpdateFileLocations and Signature file location.
- In Debug build it creates UpdateManagerConfig.xml file if not present
and saves the default configuration data. The same file can be used to
redirect the update location to the dev S3-bucket from a release build.
Fixed loading bug in Revit, allowing proper migration of PolyCurve.Fillet
Make face selection tests more stringent.
Addressing review comments
Revised methods and new tests
Merge branch 'master' into MAGN-4051
More tweaks, improvements
Fix merge failures
created CustomNodeIcon on StartPage
Add model file
Another test for nested family instance
Change as feedback
Adding testcase for UpdateManagerConfiguration
Rename GCAnonymousSymbols() to GCSymbols() and some cleanup
Remove callsite gc root
Update test cases for verifying reference count
Using RuntimeMemory.PushFrameForGlobals() to extend stack for global variables
Handle the case that expected value is null
GC deactivated symbols