When there are no filters, we can get the total todos count from the cached
count on the user object, instead of performing a DB query. This query takes
about 80ms for me on GitLab.com.

TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

[9.3 security fix] Renders 404 if given project is not readable by the user on Todos dashboard

See merge request !2118

Instead of an integration test that creates 101 Todo records to test a
simple view helper, just unit test the helper.

This reverts merge request !10845

TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

Fix for three open redirect vulns using redirect_to url_for(params.merge)))

See merge request !2082

This reverts merge request !10076