SHORTEST_PATH: Improvements to adding/removing POIs/walls.

- Trying to add a POI too near a wall now causes a warning.
  Adding a wall removes POIs in vertices that it blocks and
  informs the user about it. Added functions to FleetManager are
  bool isBlocked(QPointF* point) and bool removeBlockedPois().
- overloaded calcPath to have version that gets a POI and stores
  it in destPoi_. When it is reached, FleetManager is called to
  destroy it
- removed checkPoiCollision as unneeded
- changed driving keys to be less annoying. A and D are now for
  turning in place. E and R use radial turning.
SHORTEST_PATH: go2Poi -> go2Pois + go2Poi(*poi)

- Divided go2Poi into go2Pois and go2Poi. go2Pois calls
  go2Poi for each POI, until there is no ready Roomba left.
- A task list for Roombas is needed to allow them to collect more
  POIs than there are ready Roombas