List.UniqueItems now works for all objects
unit test
Merge branch 'master' into uniqueitems-fix
list.uniqueitems now falls back on object.Equals
removed unused code
Merge pull request #2056 from Steell/uniqueitems-fix

List.UniqueItems now works for all kinds of object: MAGN-3907
Updated codes as suggested by Yuke, Randy, Ian and ReSharper.
Merge branch 'master' of https://github.com/DynamoDS/Dynamo into Concurrent