Implement right sidebar option as user option

Currently an admin can set the "sidebarRight" option, but the user is unable to change it for themselves.

This option felt like a natural fit, and I currently use it already on my instance.

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Added a quick settings to timeline header for easier access
 - Added option to mark posts as sensitive by default
 - Added quick filters for notifications
+- Implemented user option to change sidebar position to the right side
 
 
 ## [2.3.0] - 2021-03-01