Display last activity and created at datetimes for users in /admin/users

Description

It's possible to view a user's last login time by going to the Admin panel and the User management page and then clicking on each individual user. But this is cumbersome if you want to block/delete users based on their last login.

Proposal

• Show each user's last_activity_on and created_at as a sortable column in /admin/users.

• Move the search and sort field below the filter tabs such as with issues - also move the New user button to be inline with the tabs - until lower breakpoints.

• Add last_activity_on (oldest + recent) as sorting options