add dummy device to greatly speed up tests!
add tests for group deletion
Merge pull request #2160 from aronasorman/delete-group-tests

Delete group tests
in tests: wait longer for the facility or group deletion to happen
Fixes pct_mastery for groups to show %, not fraction.
Merge branch 'release-0.12.0' of github.com:learningequality/ka-lite into release-0.12.0
Merge branch 'release-0.12.0' into control_panel_fixes
Fixes button disabled toggling.
Prevents 'Ungrouped' from being selected in group control interface.