Create new tag

[inhaledesign]

Is your feature request related to a problem? Please describe.
Users should be able to add their own tags.

Describe the solution you'd like
There should be a 'new tag' button on the Shop page that allows the user to add a custom tag. These tags should all show in a single group. This will be complicated, because they'll want to be able to delete tags they've added as well. We need to handle what happens when there are zero active_tags for these tags.

Describe alternatives you've considered

Additional context