Set at least icon theme before gnome-settings-daemon start

Else, the battery icon is not updated.

One way to do that and also remove ugly fixes would be to run tails-activate-win8-theme from tails-prepare-win8-theme using sudo as suggested by anonym.

Feature Branch: bugfix/7407-early-icon-theme

Parent Task: #6342 (closed)

Original created by @alant on 7407 (Redmine)