Improve in-app media

Currently only one logo file exists. This looks crappy.

• Create new, specialized logos (App logo, in-app logo)
• Create a set of background wallpapers
• Create a set of background clips
• Write routine to randomize pick wallpapers/clips for widgets

The set creation can/should be done by @JochemBraakhekke / @ Timo / @ Larissa; Embedding by @gahrb

Advanced: (maybe new issue)

• Pull wallpapers and clips from server for an automatized routine