Collapse left side bar in the Web IDE

Problem to solve

The left sidebar of the Web IDE can occupy valuable screen real estate on smaller screens. This can make it harder to navigate the content in the files and harder to view all of the changes.

Proposal

The left side bar (with the file tree/ edit, review, commit tabs) should be collapsible in a similar way to the right sidebar. Currently the right sidebar is collapsed by clicking on the icon for the open tab.

The icons should remain visible so that they can be re-opened to navigate back to the tabs.