Feature: add possibility to delete tags and rename tags

[miggia]

TL;DR it would be awesome to have a way to delete tags that are no longer used; it would also be useful to rename tags.

The context

Our organization switched to Fizzy from Jira last month.
We have 4 silos (a mechanics team, an electronics team, a maintenance team, and a software team).
Each team tracks its tasks with a silo-specific board.
We use project tags to track tasks across multiple teams, but this is getting out of hand because as the number of projects increases so does the number of tags.

Possible solutions

It would be useful to have a way to delete tags that are no longer in use.
An alternative could possibly be to swap projects and silos, and have project-specific boards, and silo-specific tags.
This however leaves us with the problem that we'd be left with a bunch of old unused tags; then again it would be nice to have a way to delete tags that are no longer used (or delete everything and start from scratch with a clean slate).

Other thoughts

In general I think it would be nice for Fizzy to support either silo-based or project-based task tracking, and not enforce a particular workflow.
It can happen that a given tag is typed in wrong and currently there seems to be no way to rename it; it would be great if there were.