'Adds a new cell to a table.
It will be located at current position: (``self.row``, ``self.col``).'

def add_cell(self, height, width):

    self.cell_id += 1
    for col in range(width):
        for row in range(height):
            assert (self.cells[((self.row + row), (self.col + col))] == 0)
            self.cells[((self.row + row), (self.col + col))] = self.cell_id
