Documentation cleanup
Remove AltGr from the list of ignored modifiers

(It should only be ignoring locking modifiers like CapsLock and NumLock)
Add a doc comment about the state of wnck window gravity support
Add a "minimize" command.
Add a "bordered" command to toggle window decorations.
Switch to gtk.accelerator_parse() for looking up keycodes (incomplete)

- It is now possible to specify additional modifiers in the [keys] section
  to allow things like Ctrl+Alt+KP_4 being tiling and Ctrl+Alt+Shift+KP_4
  being moving to another workspace.
- Should remove the need to manually import keysym groups outside latin1
  and miscellany
- Supports more familiar aliases like Alt instead of Mod1 and Ctrl instead
  of Control.

Also, in the process, I made the validity checks more granular and helpful.
Finish changing keybinding parser and encapsulate it in a new class.