Enabled-indicator while recording

The MusE-plugin-GUIs shall display a small LED displaying whether a controller is currently enabled or disabled. By clicking this LED, the enabled state shall be switched.

Furthermore, there shall be a dedicated window which only lets you switch enabled/disabled states. This will be useful when using external GUIs or the MIDI-controller-to-automation feature, to re-enable a controller when in fterfirstA`A=95 _ `A=58 : A <`<=95 _ `<=58 : < u@nderscorehyph<271>>UTO_TOUCH mode.