Completed adding button monitor feedback for midi controllers

[ditcheshurt]

I though it would be visually helpful for users of Midi controllers that have back-lit or otherwise feedback enabled button midi controllers to see what functions that have been activated by another function (monitoring) to create the same visual feedback you already have with the virtual console buttons.

I'm using an Akai APCMini for testing these changes and wanted to contribute to this amazing software and project.

[yestalgia]

This would fix the MIDI use case I mention here #1413

[yestalgia]

https://www.qlcplus.org/forum/viewtopic.php?t=12839

Another request for this feature

[coveralls]

coverage: 31.974% (+0.02%) from 31.958%
when pulling 863c0ae on ditcheshurt:master
into fa51c43 on mcallegari:master.

[mcallegari]

I finally merged this and found a few errors:

• the word "Value" was removed from labels (luckily I saw this)
• the monitoring spinbox was visible also for non button widgets

Now it's fixed. Thanks for contributing.

[yestalgia]

Huge improvement! Thanks guys :)