* issue content history
* Use timeutil.TimeStampNow() for content history time instead of issue/comment.UpdatedUnix (which are not updated in time)
* i18n for frontend
* refactor
* clean up
* fix refactor
* re-format
* temp refactor
* follow db refactor
* rename IssueContentHistory to ContentHistory, remove empty model tags
* fix html
* use avatar refactor to generate avatar url
* add unit test, keep at most 20 history revisions.
* re-format
* syntax nit
* Add issue content history table
* Update models/migrations/v197.go
Co-authored-by: 6543 <6543@obermui.de>
* fix merge
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lauris BH <lauris@nix.lv>
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