[feature request] incremental values for everything numerical

[lmerkens]

A lot of actions modify numerical values in obs. x|y position of a video source. crop margins. volume of audio sources come to mind. Currently we can set those values to either a fixed value or to something based on the velocity of the midi signal.
But we don't have the current value of the actions target value. A variable concept would help here, but thats probably a little bit much to ask for. An intermediate solution could be to allow to give a delta to the old value. (change the old value by a given value)
A midi key binding with an action Video Source -> Move Source -> X**+5** (increment 1) would allow to repeatedly nudge a source 5px to the right.
Video Source -> Move Source -> X-5 would give a nudge to the left.
Something similar could be done to increase/decrease the volume of a audio source, if your midi controller has no faders to work with.

just a thought and thank you for the good work on the plugin!