Remove try catch on node eval.

Try catch on node eval was causing serious performance issues for workflows where nodes were called recursively.
Add a migration to color range node to set laceability.
MAGN-820. Add a migration to support lacing on color range node.
Threading patch for validate connections

Temporary fix to address launch hold issue:
http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-847

All tests pass successfully, this needs factoring into the correct
threading model
Adjust previous fix

So that behaviour in the absence of UI is unchanged