[WIP] Splashscreen

Trying to get a splash screen working.
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. Not sure why this happens, 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 should be drawn, a progress bar or other elements.

Currently I only draw some text using the design of the looking glass inspector.
The current initialization sections are mostly for testing, nothing final.