postmarketOS settings UI

How about we implement something similar to Android's settings menu, searchbar on top, multiple categories with settings inside, for postmarketOS specific settings.

What we could put there:

• audio settings (see my music player use case)
  • automatically resume playback when connecting headphones
  • invert the volume buttons (on the n900, these seem to be inverted compared to the Android phones?)
• update settings
• developer options
  • display dmesg/syslog (open a terminal and run dmesg/logread?)
  • enable/disable sshd
• about dialog
  • display deviceinfo etc.

The program would write all settings that differ from the defaults to /etc/postmarketos.conf. That file should be easy to edit by users (so something like the deviceinfo format). The file is not provided by any package, so we don't run into updating problems with that.

Users could open the settings menu from the power button (#134 (closed)) or from the UI's application menu (we can provide a .desktop file so it fits in there).

I would like to implement the UI in something like KDE's Kirigami. However, it should perform well on the N900 and on downstream kernel devices without gpu acceleration (not sure if that is the case with Kirigami).

CC: @bshah