Phabricator currently has global "Notifications" and "Messages" items, in the top menubar. We should add a similar item for Phrequent, to serve as a global status indicator about time tracking.

When the user isn't tracking anything, the user doesn't have access to Phrequent, or Phrequent is not installed, the menu shouldn't be present. We might make it dim for the "untracked" state eventually, but for now I'm worried about distracting users with a rarely-used, barely-functional global item.

Initially, this could just show things you're currently tracking. In later iterations, we could put controls in the menu (e.g., stop / pause tracking).