Removed description edit UI / endpoints and put unified base settings form in repository settings page. This form is restricted to `repo:owner` permission same as before. The internal model of topics is an array but they are stored/edited as single string where each topics are joined with whitespaces. Having a dedicated topics table with M:M relationship to the repo seems a bit overkill considering we will have external search indexer anyway. Signed-off-by: Seongmin Lee <git@boltless.me>