Update CHANGELOG with 2.8.0 release notes
+### 2.8.0 (2019-09-19)
+- Criteria & Repositories API
+- Not a bugfix release yet, expect more bugfixes in future 2.8.x versions
+
### 2.7.4 (2018-12-26)
- Bugfix and refinements release! Thank you issue reports and PRs!
- Notable stuff
