Adds a new app menu for creating a new workspace or switching to an
existing one. This required adding a new WPS event any time a workspace
gets updated, since the Electron app menus are static.
This also fixes a bug where closing a workspace could delete it if it
didn't have both a pinned and an unpinned tab.
This migrates all remaining eventbus events sent over the websocket to
use the wps interface. WPS is more flexible for registering events and
callbacks and provides support for more reliable unsubscribes and
resubscribes.
