Allow having the UrlNavigators below the tab bar

Allow having the UrlNavigators below the tab bar

This commit restores the possibility to have the UrlNavigators below
the tab bar. This will happen automatically whenever the UrlNavigator
is removed from the toolbar.

It is also now again possible to have the toolbar on the side. This
option is disabled while the toolbar contains the UrlNavigators.

This commit makes no changes to the new default which is having the
UrlNavigators in the toolbar but makes sure that upgrading users won't
be affected.