SHORTEST_PATH: initial vertice implementation (not compiled) + MAPWIDTH

- vertices_ now holds all vertices properly linked to each other.
  Implementation is an initial uncompiled version
- added constant Util::MAPWIDTH with value of 400
- replaced magic values with it (402 with Util::MAPWIDTH+2)
  so the map is now 2 pixels larger in both directions
SHORTEST_PATH: verticeconnections now follow wall addition/removal
SHORTEST_PATH: vertices updated for Dijkstra and algo started
SHORTEST_PATH: Added vertices and shortest path algorithm

- Vertices added. Adding walls breaks connections and removing
  walls renews the broken connections.
- Shortest path is now calculated with Dijkstra's algorithm
  (in calcPath function) and the path_ is stored in IRoomba. The
  function's return value is the length of the path.
-  Adding/removing walls seems to work with vertices but the
   calcPath is untested
SHORTEST_PATH: fix to verticeconnections when removing walls

- now connections to vertice are renewed when the wall to be
  removed is in its area but no other wall is.
- for implementing above functionality, I added reimplementation of
  type() -function to PoiQGraphicsEllipseItem and
  WallQGraphicsLineItem