close floating sidebar on escape

[mbostock]

This small enhancement makes it so that when the sidebar is opened in floating mode (with a drop shadow), Escape will close the sidebar in the same fashion as clicking on the backdrop. (Note that this sidebar can either be opened persistently with Command-B, or temporarily opened with Command-K.)

[Fil]

Of note, on a small screen with the search field focused, this means we now need to hit Esc twice: to empty the field, then to close the sidebar. I'm fine with this new behavior (which feels less surprising, in a way).