main/postmarketos-ui-mate: improve touch-friendliness (MR 5713)

Maintenance:
- Renamed gschema override files for "system background" and "screensaver"
  to prefix number "10", that's more common for distribution-delivered
  gschema override files. Basically the prefix number just separates the
  override files from the xml files.
- For gschema override files "caja single click" and "mate terminal colors"
  replaced underline by dash character for better alphabetic sorting.
- In the APKBUILD, adapted the install of file "gtk.css" to the "-t" option,
  as no file name change is needed.
- Sorted the installs alphabetically per path, except the for the file
  "61-lightdm-autologin.conf", this one is at the end because it doesn't use
  the "-t" option due to file renaming.

Touch-friendliness:
- Increased size of the upper and lower panel from 24 to 36 px. This also
  increases the size of the icons in the panel. Unfortunately, at installation
  the panel layout config file is stronger than the gsettings override of the
  panel size, therefore a new panel layout config file is needed. It corresponds
  to the upstream default layout, just the panel size values were changed.
- Increased the size of the window buttons by changing the window border theme
  to "HighContrast". That's not the nicest looking theme but the one with the
  largest window buttons – convenient for touch devices.
- Increased general font sizes from 10 to 12 px. This goes along with increased
  panel size and window button size, avoiding looking it too unproportional.
- Changed the layout of the panel clock to just show the time (no date or week
  day). This saves space on devices with small screen. As the panel size was
  increased, display size gets tight on devices with small screen.
- Changed the layout of the panel workspace switcher to show names in the format
  of "-  x  -". This is a workaround to artificially increase the size of the
  workspace switcher buttons on portrait displays. Because otherwise these
  buttons are very squeezed on portrait displays due to the display ratio.
- Add an application shortcut for a maximized terminal to the users Desktop
  upon installation.
[ci:skip-build]: already built successfully in CI