This branch:
- Refreshes Glade files for version 3.38, bumps GTK minimum version to 3.22, libxfce4ui to 4.12, and replaces deprecated values and widgets
- Improves spacing according to the 6/12/18 standards from the GNOME 2 HIG (and used elsewhere in Xfce)
- Removes unnecessary newlines in the Tweaks window
- Adds right margin to slider labels on the Compositor tab
- Cleans up order of generically-named (e.g.
label1) widgets for easier future review
Closes old pull request #299.