Add UI for power room control point

[jamesremuscat]

We're going to reinstate the A/V control point in the power room. While we could just reuse the same UI as on the operator touchscreen, we might want to develop a more specific interface.

Some thoughts:

• There's no point in being able to control cameras without being able to see their output
• Some form of system status (e.g. relay states, router states) would be nice, as would making the application logs accessible
• Could still operate switchers, blinds, screens
• Admin features to restart avx-controller process and/or the av-control host machine?
• The new touchscreen has both VGA and composite inputs so we could wire it up to the Extras switcher as an additional preview output?

[rjmunro]

On your last point, can you still use it as a touch screen when it is in composite mode?
Can you control or read which input it is using from the computer that it's touch control is wired to? If yes, interesting things become possible...

[jamesremuscat]

I suspect that the answers are yes and no respectively, but I'll find out when the touchscreen arrives and I get the chance to investigate!

[jamesremuscat]

The answers were yes and no, respectively.

This work still needs to be merged from feature/power-room-control.

[jamesremuscat]

The feature/power-room-control branch is probably rotting - it doesn't include any of the changes made as part of the HD upgrade. It might be salvageable!