Provide a list of existing tags at tag creation and editing

Every time a user is actively interacting with the site's tags (creation, editing) a list of tags already in use should be available, for reference or use.

Currently a list of tags is displayed when filtering pages for tags (https://we.riseup.net/groups/example-group/pages/#/). Maybe that be reused for this purpose?

Ideally, a click on a present tag would associate the current file with it. Auto-completion for partially typed tags would be awesome.

Thanks so much, we love you guys and gals!