Modify tests to verify that Add Card button is visible in the action bar after deleting cards
Fix bug where CAB didn't entirely disappear.
Modify `testMarkAll()` and `testUnmarkAll()`

Improve `testMarkAll()` to assert that all list items are checked. Clean up
 `testUnmarkAll()` to assert that **all** list items are not checked rather than
 only counting how many **visible** list items are not checked.