* Allow mounting arbitrary columns
* Refactor column headers, allow pinning/unpinning and moving columns around
* Collapse animation
* Re-introduce scroll to top
* Save column settings properly, do not display pin options in
single-column view, do not display collapse icon if there is
nothing to collapse
* Fix one instance of public timeline being closed closing the stream
Fix back buttons inconsistently sending you back to / even if history exists
* Getting started displays links to columns that are not mounted
