SHORTEST_PATH: "Stop Fleet"-button + small autocapture change

- "Stop Fleet" makes all Roombas to stop and resets everything
  related to following a path. FleetManager's stopFleet() calls
  stop() for every Roomba. Any additions to fleet management
  and roombas will need to have a corresponding reset implemented
  in these functions.
- Changed the order of setting autocapture interval and starting
  autocapture in RoombaRoowifi. The time is still 500 ms due to
  increasing inaccuracy at smaller intervals. The best compromise
  needs more testing (and taking floor material into account)