What the user code needs to implement

1. actions (optional)
	StatusSetText()
	DescribeLocation()

2. docked DAD subwindows (optional)
	bottom status line
	top right coord readout
	top left toolbar

3. conventions
	all calls have access to the current (pcb_hidlib_t *)
	there's a design (pcb_board_t)
	recommendation: the design struct's first field should be pcb_hildib_t so they can be casted forth and back

4. icon colors:

	None    - transparent
	#000000 - black
	#7A8584 - light grey
	#6EA5D7 - cyan/blue
