Attempt at CO aliasing (not working yet)
We don't need to check if the alias has a creator
Create a method inside MixxxMainWindow for initializing aliases and call it before loading the skin and initializing controllers
Introduce a new mutex to guard access to s_qCOAliasHash
Rename createAlias to insertAlias
Add unit test for alias retrieval
Merge pull request #283 from badescunicu/co_alias

Add Control Aliasing