Changelog entry for issue page speedups

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.1.0 (unreleased)
+  - Speed up load times of issue detail pages by roughly 1.5x
   - Make diff file view easier to use on mobile screens (Stan Hu)
   - Add support for creating directories from Files page (Stan Hu)
   - Allow removing of project without confirmation when JavaScript is disabled (Stan Hu)