Sentinel Linux desktop/boot hotfix 1.0.1-1

Scope:
- preserves corrected GRUB title/background and quiet Plymouth splash;
- removes the erroneous requirement for uninstalled coloured GTK/Marco themes;
- prevents the cursor synchroniser from writing the icon-theme key;
- provides an optional icon-only selector for the five installed icon colours.

Full coloured GTK/Marco theme expansion is deferred to a later visual QA phase.
No applications, security rules, repository policy, wallpaper or panel layout are changed.
