1. Updated "NodeModel.ValidateConnections" to not remove "ElementState.ERROR"
2. Introduced "NodeModel.ClearError" method to compliment "NodeModel.Error" method
3. Updated "NodeModel.State" property setter to not raise change event if reporting is off
4. Updated various codes that call "Error" method to also call "ClearError" for success case
5. Updated "Formula.FormulaString" property setter to raise "State" change event
Added unit test case "ValidateConnectionsDoesNotClearError" for defect verification
Merge pull request #887 from Benglin/StatesAndReporting

Fix MAGN-919 Errors disappear if user clicks on the node