Unset force reexecute if watched elements not modified or deleted.
Add two tests.

These tests ensure that the graph stays in sync with the model by
continuously deleting elements in the model and checking the counts
against what is expected in the graph.
Merge remote-tracking branch 'origin/master' into SelectionForceReexecute
Move force reexecute flag set to end of execution.
Merge pull request #2703 from DynamoDS/SelectionForceReexecute

Unset force reexecute if watched elements not modified or deleted.
Merge remote-tracking branch 'origin/master' into SolarRadiation