Add hint text to navigation drawer

Currently, when no tags exist, the tags section is hidden in the navigation drawer. Let's add some hint text in place of it to indicate that tags will appear there.

- If no tags exist then hide "Edit" button
- If no tags exist then show hint text

Start by locating the iOS navigation drawer and the code that renders its tags section. Verify the empty-tags state, then confirm that the Edit button is hidden and hint text appears where the tags would normally be. Done means the drawer clearly indicates where tags will appear when none exist.

Written by the indexing model from the issue text.