Add Support for custom keyboard Shortcuts

[Robert-112]

Hello,

in some cases it is usefull to have cutom keyboard Shortcuts.

In my case i turned the monitor off with display-off.sh an than a node-js-script waits for websocket-call to turn on the montior with display-on.sh. That works great.
(for HDMI-TVs i used cec-on.sh and cec-off.sh)

But i found no way for the user to turn on the monitor by himself.

Since Matchbox is used as window-manager, i found a way, to lauch scripts with a keyboard-shortcut.

Therefore i did the following steps:

• create a file `~/.matchbox/kbdconfig'
• edit the file kbdconfig and add the following lines
• <ctrl>n=!/home/pi/display-on.sh
• <ctrl>b=!/home/pi/display-off.sh

(more exampels can be found in /etc/machtbox/kbdconfig)

After reboot i can turn on the mointor with CTRL+n an can turn it off with CTRL+b.

These shortcuts (or other) should be available in the image by default.