When a site does not have `default_navigation_menu_tags`
site setting set, anonymous users should be shown the site's top tags as
a default in the tags section. However, this regressed in 9fad71809c254752479b0faf4f23ba197e742e60
and we ended up showing anonymous users a tags section with only the
`All Tags` section link.
As part of this commit, I have also refactored the QUnit acceptance
tests to system tests which are much easier to work with.
