GNOME Sudoku 50.beta

• Add save, export and share shortcuts to the shortcuts dialog
  
• Fix loading finished games failing when the timer was disabled
  
• Fix reset board being unhooked
  
• Fix shared game not always being correctly detected
  
• Fix natural window width being higher than 360
  
• Fix reference cycle
  
• Update translations:
  Ekaterine Papava (ka); Baurzhan Muftakhidinov (kk); Aurimas Aurimas
  Černius (lt); Juliano de Souza Camargo, Rafael Fontenelle (pt_BR);
  Sergej A. (ru); Martin (sl); Emin Tufan Çetin (tr); Yuri Chornoivan
  (uk); luming zh (zh_CN).