Changelog 1.15.3 (#17091) (#17113)

Changelog 1.15.3 (#17091) (#17113)

## [1.15.3](https://github.com/go-gitea/gitea/releases/tag/v1.15.3) - 2021-09-19

* ENHANCEMENTS
  * Add fluid to ui container class to remove margin (#16396) (#16976)
  * Add caller to cat-file batch calls (#17082) (#17089)
* BUGFIXES
  * Render full plain readme. (#17083) (#17090)
  * Upgrade xorm to v1.2.4 (#17059)
  * Fix bug of migrate comments which only fetch one page (#17055) (#17058)
  * Do not show issue context popup on external issues (#17050) (#17054)
  * Decrement Fork Num when converting from Fork (#17035) (#17046)
  * Correctly rollback in ForkRepository (#17034) (#17045)
  * Fix missing close in WalkGitLog (#17008) (#17009)
  * Add prefix to SVG id/class attributes (#16997) (#17000)
  * Fix bug of migrated repository not index (#16991) (#16996)
  * Skip AllowedUserVisibilityModes validation on update user if it is an organisation (#16988) (#16990)
  * Fix storage Iterate bug and Add storage doctor to delete garbage attachments (#16971) (#16977)
  * Fix issue with issue default mail template (#16956) (#16975)
  * Ensure that rebase conflicts are handled in updates (#16952) (#16960)
  * Prevent panic on diff generation (#16950) (#16951)

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>