Add dependency on Python termcolor package
Stop failing when gsettings is not installed

gsettings is an optional dependency. When subpixel antialiasing rotation
is enabled and gsettings is not installed, thinkpad-rotate should warn
the user, not fail.
Add support for subpixel rotation in XFCE
Warn about missing external screen when docking

Before, `thinkpad-dock on` would fail if the external screen was not
found. Now, a warning is issued instead.
Add Debian package name and footnote
Merge remote-tracking branch 'jturner314/fix-subpixel-call'
Merge remote-tracking branch 'jturner314/fix-screen-edge-case'