Decoupled Mediator/Command from Actor so DIUtil was not a dependency was Mediators/Commands.

This was done to make unit testing easier on these elements.
Fixed bug with Mediator mappings not working correctly when declared with an Interface.
Added MapInstanceToSingleton and UnmapInstanceFromSingleton to the DI Container.
Added a dictionary key check for UnMapSingletonInstance and added UnMapSingleton method.
Updated Invoker class to instantiate Commands each time Invoke is called instead of holding onto an instance.

Commands should be executed and then discarded.
Added a couple of tests to confirm I could use Invokers like Signals in Swiz/RL. Updated MapCommandToInvoker to return a TInvoker so I could invoke it all on a single line.
Added a test for invoking inline with map to command.