Alter Marionette.normalizeUIKeys to return a new/non-mutated hash

Instead of mutating the original argument hash, create and return a new cloned hash
Addresses issue #1728
take a look at the other unit test files and try to follow their style. 

define your vars and do you setup actions in the beforeEach hooks
assert the result of the behavior in the `it` block

Let us know if you have any questions in chat :)