Add stub tests for document switch events.
Make CurrentUIDocument settable.

Our document switching behavior changed because we made the document
manager get the currently active document. Instead, we want the old
behavior where Dynamo's current document was set and only re-set in
certain limited situations during view switching.
One more stub test for document switching.
Cleanup and notes on DynamoRevit

Make sure Dynamo button is re-enabled during a crash.

Add a conditional re-enablement of the run button when switching between
documents.
Document switching logic on revit controller.

Adjust document switching logic to maintain reference to initial
document, except in the case where all documents have been closed and a
new one has been opened.
Keep geometry conversion on viz thread.

Geometry conversion should remain on the viz thread. Only pushing the
geometry to the view should be on the UI thread to avoid locking the UI
for the time it takes to do the conversion.
Do not update viz manager during...

Un-connection of connectors.
Deletion of a node.

This is a performance improvement which has the effect that geometry
belonging to nodes affected by those changes does not get cleaned up.
That geometry will only get cleaned up during the next evaluation.