Community lookup consolidation

Expected

As users are never sure how a community name is written/addressed correctly, Piefed should be most tolerant and helpful.

A user should be able to quickly recover from typos/errors through Piefed's assistance.

Pre-filters for results should be absolutely transparent.

Actual

• There are many ways and completely different UI/UX for community lookups:
  1. https://piefed.social/communities
  2. https://piefed.social/search (community filter tab)
  3. That "Communities" dropdown on every page's head ¹
  4. Post composition (usually pre-assigned because Create Post buttons are on community pages) ¹
  5. When linking to communities in text compositors.²
  6. When moving a post³
  7. When cross posting, the user got prompted for a leading "!" until recently.³

• There's no assistance in the Feed editing view. ⁴
• When typing the wrong address e.g. piefed.social/c/piefed_meta_with_typo the user is forwarded to the community creation form, not to a lookup page.

I did not check which of those support lookup by name (url) and/or title. Of course, both should be supported.

¹) Restricted to joined and moderated communities (full list!)

²) User has to type "!"

³) UI freezes after typing "!"

⁴) "!" is not allowed but should be tolerated.