Shortcut validator now uses ASCII keys by default.
Add method to create shortcut from key code and modifier flags.
Fix allowsEmptyModifierFlags is not taken into account.
Fix recording may start event when window is not key.
User proper glyph for the space key.
Fix various aspects for key equivalent transformers.

Use recognizable by Cocoa glyph for keypad enter.
Ensure shift mask is appended if key code is special.