Shelf support

[heathbishop]

trafficstars

Please add support for shelf. The ability to shelf changes and unshelve them later is wonderful when your bouncing back and forth between request and tickets. It would be amazing to have an implementation similar to WebStorm's. Essentially another collapsible panel (like REPOSITORIES, FILE HISTORY, and BRANCH HISTORY) that simply showed the names of each shelf with the arrow option to collapse and expand the shelves. Similar to REPOSITORIES and FILE HISTORY.