This PR do some performance optimzations.
- [x] Add `index` for the column `comment_id` of `Attachment` table to
accelerate query from the database.
- [x] Remove unnecessary database queries when viewing issues. Before
some conditions which id = 0 will be sent to the database
- [x] Remove duplicated load posters
- [x] Batch loading attachements, isread of comments on viewing issue
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Co-authored-by: Zettat123 <zettat123@gmail.com>
Lunny Xiao