Excluded tag filters

[aiosk]

My attempt to add Excluded tag filters.

Example:

filters:
  tag: tasks
  -tag: archived
columns:
  - name: Backlog
    backlog: true
  - name: Ongoing
    tags:
      - wip
  - name: Done
    completed: true

will add test case later

[PackElend]

@aiosk we are still searching for a new maintainer but as you are familiar (a bit) with the codebase of the plug-in would are ok with checking the other PRs. I can't call myself experienced enough, but if some of the others would check each other's PRs, it can be said that the code is safe, so I merge it. At least there would be some progress thx