Dynamo Package Path should be retrieved from loaded params not startup params

[alfarok]

For Viewport to be installed and run after the initial Dynamo startup the Dynamo Package Path must be retrieved from the loaded params instead of the startup params. Failure to do so will results in the Viewport not loading correctly and will require a restart of Dynamo. The default package path was recently added to the loaded params in a Dynamo PR.

Changes should be implemented in ViewportViewExtension.cs