Replaced array with vector

A vector is a better way of storing contiguous objects than array
as it can expand if necessary, has the same fast access as an array
and doesn't have to maintain empty cells. You should use vectors in
most cases as they provide iterators that allow them to use standard
algorithms as well.

* Have a look at the loops how simpler they are as you only iterate over
  valid elements.
* In the old ChessBoard::save(..) you used "Iter" which wasn't like an iterator
  as it was making a copy of the piece (iter = this->white->getPieceInfos(i);)
  It would have worked if you used Iter*. In that loop you were also getting the
  piece multiple times (once to check it existed, then to make a copy).
* You can use some tricks to make the init a bit cleaner, see the new version