{KeyCounter -> InputCount}Controller
KeyCounterDisplay
This allows to keep a coeherent state regardless of the progress of the play
CompositeDrawable
I also took the freedom to add type checking, as we can't limit the usage of `Add()` since it's a Container. The exception thrown also advises of using the suggested `AddTrigger()` instead.
`IsCounting` is back being an auto-property. `countPresses` is now encapsulated and being exposed as an `IBindable<int>` via `CountPresses`
TestSceneAutoplay
ReplayPlayer
SongProgress