Changing width / height of a MIDI controller is not updating the mapping

## Issue description
When you change the width / height of a MIDI controller, those values are updated, but the resulting mapping is not. 

## Steps to reproduce
* Add a MIDI controller with width = 2 & height = 2
* Change the width to 4
* See that the layout of the MIDI controller still is a 2 by 2 grid

## Versions

1. Browser: Chrome 72
2. luminave: 3.1.0-dev
