Allow maximising the main window about minegauler HOT 2 OPEN

This is kind of horrible to get working properly :)

• Maximise button should be enabled (easy)
• Default size should be the tight fit around the board (or with scrollbars if the board is bigger than the max window size)
• When changing the board size (via dimensions or button size):
  • If the window is maximised it should stay maximised
  • If the window is not maximised and does not have any scrollbars it should be set to the default size
  • If the window is not maximised and has scrollbars it should be set to:
    • the tight fit around the board for dimensions where this is smaller than the current window size
    • unchanged for dimensions where the size is bigger or equal to the current window size
• Ideally it would not be impossible to increase the window size beyond the tight fit. However, the naive approach prevents maximising the window [on Windows].
  • A less satisfactory alternative would be to reset to the default size when selecting the current difficulty (not including selecting a custom board of the same size), which can be done with a single keyboard button press (e.g. 'b').
• Persist window state:
  • Whether maximised
  • The dimensions of the window (or displayed size of the minefield?)
• The name bar should be strictly along the bottom, with padding being around the minefield frame such that the minefield is in the center of the space

from minegauler.

Enabled in beta options in PR #125, although buggy and state not persisted.

from minegauler.