Updated "ConnectorModel.Make" method to take "PortType" instead of "int"

#### Background

Updated "ConnectorModel.Make" method to take "PortType" instead of "int". The reason for this is because it makes the method more self explanatory and caller must explicitly specify "PortType.Output" instead of "1", which is much less likely to get wrong.

#### Test scenarios

The following are a few scenarios for testing (I have tested most of them to ensure the code changes do not break anything that they affect).

1. Open custom node should retain the connectors
2. Open regular Dynamo file
3. Establish a new connector
4. Undo and redo connector's creation
5. Collapse a set of node in a given workspace

#### Unit testing

All existing NUnit test cases passed: DynamoPythonTests, DynamoCoreUITests, DynamoCoreTests, DynamoMSOfficeTests, DSCoreNodesTests.