Show current filters on frontend

[IllyaMoskvin]

Blocked by #19. Related to #45 and #27. Proposed by @dylanirlbeck in #45:

It'd be nice to also have a banner of some sort that indicates if the extension is applying the filter, and if so what the filter is for (e.g. Black History Month).

We chatted about this internally, and we think that a good way to go would be to have some sort of hamburger icon in the top-right corner. When activated, it should open a drop-down menu with a list of filters. This menu is informational: these filters do not need to be editable from within the menu directly. At the bottom of the menu, there should be a link to the plugin's settings, where the user can edit the filters.

We might work with our designers on a mockup for this functionality, but it's not a blocker. For anyone interested in this, once initial work on #19 is complete, this ticket is up for grabs. As long as the code is clean and works well, we can do a design pass after the functionality has been implemented.