Req: add 'default' catchall to remappings

[mmazur]

I've seen discussions where people mention that using remappings disables a given modifier key for any use outside evdevremapkeys.
A simple and elegant solution to this would give the option of defining a default catchall that would be applied any time an explicit key combo is not defined. Proposed syntax:

  modifier_groups:
    caps:
      KEY_H:
      - KEY_LEFT
      KEY_J:
      - KEY_DOWN
      KEY_K:
      - KEY_UP
      KEY_L:
      - KEY_RIGHT
      default:
      - KEY_LEFTMETA
      - KEY

Additions:

• default – execute whenever the modifier was not used with an explicitly defined key
• KEY – resend the key pressed

With the example presented above caps+hjkl works as vim–like navigation everywhere, while on a typical desktop environment e.g. caps+d would be "show desktop" and any other caps+KEY would be easily boundable via your desktop environment or something like xbindkeys.