Before this commit the navigation toolbar was accessible after selecting
a theme before the editor was opened, which on slow connections made it
possible for users to leave the screen and miss the tour
After this commit the loader animation of the theme installation is
blocking the access to the screen until the editor is opened thus
preventing user to navigate elsewhere before seeing the tour
task-2387608
closesodoo/odoo#62029
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>