[WIP] Splashscreen

Trying to get a splash screen working.
This currently does:
- Show some text on what is currently being done
- Show a progress bar

This test works, but there are some uncertainties:
- When logging in, there are 1-2 seconds of black screen where nothing is shown, so the splash screen can't be seen there either.
Not sure if that is actually cinnamon causing the black time or something else.
- I've noticed some issues with gnome-terminal windows becoming invisible after a cinnamon --replace.
  This seems to happen due to a bug with window bottom group.
  The mouse cursor still changes and the alt-tab preview shows the window correctly, but the window itself is invisible. This is a little random tho, sometimes it happens, sometimes not.
- Not sure if icons or other elements should be drawn.

The current initialization sections are mostly for testing, nothing final.

Note: I removed panelmenu.js since it is not used anymore.

Screenshot:
http://lusito.info/splashscreen.png