changelog(): updated with preferences features

CHANGELOG.md

 # 3.0.0-beta2 (unreleased)
 
+### New Features (introduces since 3.0-beta1)
+* **Preferences**: Set home dashboard on user and org level, closes [#1678](https://github.com/grafana/grafana/issues/1678)
+* **Preferences**: Set timezone on user and org level, closes [#3214](https://github.com/grafana/grafana/issues/3214), [#1200](https://github.com/grafana/grafana/issues/1200)
+* **Preferences**: Set theme on user and org level, closes [#3214](https://github.com/grafana/grafana/issues/3214), [#1917](https://github.com/grafana/grafana/issues/1917)
+
 ### Bug fixes
 * **Dashboard**: Fixed dashboard panel layout for mobile devices, fixes [#4529](https://github.com/grafana/grafana/issues/4529)
 * **Page Load Crash**: A Datasource with null jsonData would make Grafana fail to load page, fixes [#4536](https://github.com/grafana/grafana/issues/4536)