Pylint's `bad-classmethod-argument` is disabled for each definition
to avoid rewriting the method bodies just to rename `self` → `cls`.
This can be done gradually, as the setUpTestData methods are modified
along the way.
We should store hashtags case-sensitive, but ensures that an existing
hashtag with different case are found and re-used. for example,
an existing #BookWyrm hashtag will be found and used even if the
status content is using #bookwyrm.
Since the status content already contains rendered HTML when we receive an
ActivityPub inbox message it contains links to the mentioned hashtags on the
originating instance.
To fix this on the receiving instance we need to post-process the status content
after successfully storing the status and its many-to-many fields (the one we're
is the `mention_hashtags`). Post-processing means that we run a regex against the
content to find the anchor tags linking to the originating hashtag and replace the
`href` attribute with the URL to the hashtag page on the receiving (local) instance.
