Add new features:
1)Add QSettings in ini file with the following parameters:
  1.1. cells/width - width of cell in pixel;
  1.2. cells/height - height of cell in pixel;
  1.3. cells/font_size - font size for numbers in cells
  1.4. field/size - field size in cells
  1.5. field/num_bombs - number bombs

2) Cell now can change font size on-fly
3) Field now can change parameters on-fly
4) Add SettingsWidget for edit ini-file.