Dmxkeypad

Adds a DMX KeyPad to the simple console allowing ranges of channels to be manipulated at once and it's easier to use on a touchscreen than faders.
I don't consider this feature-complete but it should be production-ready. All commands that can lead to strange behaviour (crashes or 100% CPU load) should be impossible due to buttons beeing disabled.

TODO: 
- documentation
- add it to the webserver somehow (together with an "clear universe" button as we have on the simple console

Discussion thread: https://sourceforge.net/p/qlcplus/discussion/development/thread/6039d20d/