Made a start at getting pathfinding integrated into game.

- Modified Cell and derived classes to work as pathfinding nodes. Might
  want to use composition rather than inheritance for this in the future
  though and define the pathfinding node class as a separate class that
  can be injected into the Cell class.

  The cell get_neighbours() function acts a bit different to the example
  one as it chooses all 8 cells around a cell including diagonals rather
  than just up, down, left and right.

- Moved the python-pathfinding library into a different directory as the
  package was not accessable to our program otherwise.
Merge branch 'master' of github.com:TeamAudioplode/AudioplodePrototype