Cell - remove opened status as boolean. add flag functionality
CellStatus - introduce cell status to keep the status of the cell as
CLOSED, OPENED, FLAGGED
Grid - Add open and flag functionality, 
Game - Rename to Minesweeper
Player - introduced new class for creating the Minesweeper
RandomGridFiller - refactor CheckMineIfNotPlaceOne method 
CellsValuePopulator - refactor the interface to accomodate the grid as
argument
isIdentifiedAllMines moved to Grid