Added cinnamon gschema files
Applet appearance setting read from schema
Changed appearance setting to match previous shell extension behaviour
Made default appearance icon + duration

- Takes up less space in panel so probably a sensible default
Re-instate hotkey setting

- Will only work in Cinnamon >= 1.8
- At some future point we should move to the new Cinnamon settings API
  (once cinnamon >= 1.8 becomes widespread)
- All relevant settings now ported from shell-extension. Fixes #1