Merge branch 'fix-homepage-redirection' into 'master'

Fix redirection to home page URL for unauthorized users

Redirection to the home page URL was broken by changing the target for
`root_url` from `DashboardController` to `RootController` in
94d3c143. This regression was introduced
in the 7.12.0 release.

Fixes #1916.

See merge request !928