STORM-318 FIXED The Advanced menu shortcut was broken under Linux.

Reason: The old shortcut (Ctrl+Alt+D) was eaten by some window managers.

Changes:
- Changed the shortcut to Ctrl+Alt+Shift+D.
- Moved the appropriate menu item from "Advanced > Shortcuts" to "World > Show"
  (so that it's not in the menu it triggers) and made it visible.
  The old shortcut is still available but marked as legacy.

Submitting on behalf of Boroondas Gupte.