`allow_accepted_answer` should be `allow_accepted_answers` (with an `s` at the end) in the `TopicAnswerMixin`.
The `enable_solved_tags` setting description seemed to be using the description intended for `allow_solved_on_all_topics`. Both descriptions have been updated.
This PR adds a site setting called `enable_solved_tags`. Solved will be enabled for topics containing these tags, just like we do for specific categories.