Fixed comments
Rearranged code to reduce method complexity
Extend Grid with player property
Extend with relationship between player and grid
Removed relationship between player and cell. Use grid to get the cell
of a player.
Change relationship between Ship and Cell from n:m to 1:n
Modified Cell tests to handle changed relationship
Add status flag to Cell
Add cell initialization to Grid constructor and made relationship to
Grid as mandatory for the Cell.
Fixed style guide warnings