General Mac keyboard shortcut cleanup.
Reference: Apple Human Interface Guidelines for keyboard shortcuts.
Proposing to bind Command-O to the File->Open (.val file) function (in line with AHIG).
Proposing to bind Command-P to File->Layout->Print and Command-Shift-P to File->Layout->Print Preview (in line with AHIG).
Proposing to bind Command-Shift-D to File->Pattern Properties (in line with Inkscape).
Proposing to bind Command-Option-D to Pattern Piece->Config Pattern Piece (logical continuation of the Pattern Properties shortcut).
Low priority/severity. I hope the proposals do not clash with other language versions.