lajonss authored Jan 02, 2021 and Robert Roth committed Oct 15, 2021

In the existing layout sidebar buttons (new game, pause, clear board and
high scores) were taking big amount of screen space. When window had
a vertical aspect ratio more space was wasted above and below the
minefield. The loss of space was especially painfull on a smartphone
screen.

This commit introduces changes in layout to minimize the loss of screen
space:
- new game, pause and clear board buttons were moved to the headerbar
- high scores button was removed (the action remains available in the
  primary menu)
- clock and mines counter may be moved below the minefield if the window
  has vertical aspect ratio

Semi-related changes:
- primary menu definition was moved from vala to interface.ui
- minimum tile size was increased to 30