Better separation of concerns. Relegates `ControllerInterface` to
enumerating input controls, and the new `ControlReference` deals with
combining inputs and configuration expression parsing.
Small cleanup by using std::shared_ptr and getting rid of
ciface.Devices() which just returned the m_devices (which defeats the
point of making m_devices protected).
Incidentally, this should make the code safer when we have
different threads accessing devices in the future (for hotplug?).
A lot of code use Device references directly so there is
no easy way to remove FindDevice() and make those unique_ptrs.
We can't use RendererHasFocus for this purpose because of some issues
with exclusive fullscreen, and the new RendererHasFocus implementation
didn't work for non-Render to Main Window cases, since the renderer
window wasn't managed by wx.
Lioncash