Add UI for creating/editing tools and mapping to buttons and/or maybe keys

[bk138]

This means having a graphical tool editor (setting pen/eraser/whatever and colour and thickness, opacity, etc) and a graphical mapping editor (e.g. "mouse button 1 together with Shift triggers tool 2"). The manual gromit-mpx.cfg file editing will go away.

stop-gap solution to make finding and editing config easier

• extend default cfg
• ship default cfg with install (is the root one)
• add menu entry that
  • copies in shipped config if not there
  • opens user config
• translate

full UI solution

• tbd

[wztdream]

This feature is really great. It will be very nice if you consider following desing:
it works like this:

1. right click mouse, then pop up wheel shape menu, around pen center
2. left click menu to finish the selection
   with this design the distance for mouse movement is minimum.

[LuNeder]

The ppInk UI is really great too, maybe take inspiration from that