Little renaming, refacturing and little bug fix

1. I renamed "CountNeighborcell" method to "CountSurroundingMines". Also
renamed all his variables.

2. I renamed "CheckBoardDimensions" method to
"CheckIsThePosiotionValid". Also i make refacturing of the method, and
renaming all of his variables.

3. I add a check for the inpt for the space between row and column
input. Because without it 123 or 1a3 for example were valid inputs.