Get rid of the "importer" concept for accounts and statuses, do everything in reducers
This is an absolutely insane MR: https://github.com/mastodon/mastodon/pull/6826/files
It makes things unmaintainable. Nothing this complicated should ever happen in Redux actions. At least reducers can actually be tested. Reverting this to the prior state would greatly simplify the code.
Even worse, the offline functionality that MR added ended up being removed because it didn't work properly. That MR should have never been merged, and I'm going to try to reverse it.