[feature] enable removal of tag from current filtering

[masukomi]

when you've clicked on a tag, or used one to filter a list the icon turns into a no-entry icon so that you don't try adding it again.

this should be replaced with an x icon. click that icon should reload the page with that tag removed from the query params or url

note that a tag can appear in query params if it's a search filtered by tags (plus icon) or if you clicked a tag and then filtered it more (plus icon again), OR it can appear in the url if you've just clicked a tag (no plus icon).

the grey no-entry icon in this screenshot is unclickable. it should be replaced with a (presumably red) X that is clickable and performs the action described above.