Hiding the GUI and Control Panel

# Description:
This is a first attempt to hide the GUI/ControlPanel on a key press so that the player can take screenshots. Simply press "Ctrl+Tab" to toggle it on/off.

It draws the system path, or at least as much of it as is valid, in the top left corner and hides everything else.

# Discussion:
So this sort of does what was discussed in #1709 but it's...
* hacky,
* the text is ugly,
* seems to screw up some screens (F2 etc),
* not sure it should be exposed like it is.

Please discuss.