"Maintenance status" comment

[Akuli]

Idea: In the beginning of every .py file, let's add a comment that explains how developers feel about that file. This is important to know when you start editing a file heavily, but hard to figure out.

Some examples:

• plugins/find.py:

  # Maintenance Status (2023): Behaves exactly as intended, lots of unit tests,
  # large changes are very unlikely to pass the review.
  

• plugins/langserver.py:

  # Maintenance Status (2023): Contains various hacks. I am happy that it works
  # and also happy that I don't have to touch this code very often.
  

• plugins/blockcursor.py:

  # Maintenance Status (2023): Not changed much after it was added initially. Does
  # not do anything by default (checkbox in settings). Unclear if anyone needs this.
  

• plugins/highlight/tree_sitter_highlighter.py:

  # Maintenance Status (2023): Code looks simpler than it is. Porcupine's syntax
  # highlighting as a whole is hard, and not very well documented. To learn
  # more, look at tree-sitter-token-mappings/README.md or ask Akuli or rdbende.