Implemented save game feature

Created SudokuSaver class in sudoku-saver.vala

https://bugzilla.gnome.org/show_bug.cgi?id=633464
Patch which enables 'markasPlayedToggle' and 'includeOldGamesToggle' options in multiple print dialog

https://bugzilla.gnome.org/show_bug.cgi?id=633464