Build a shortcut help into Magnolia UI so that users can learn the shortcuts with a screen reader. Today Magnolia does not give any hints that shortcuts are available. You have to learn them by reading documentation.

Example: Twitter (see screenshot) has a shortcut reference built into the page that screen readers can "see" but is visually hidden for other users.

Acceptance criteria:

• hit keyboard "?" (shift +"?") to open Magnolia shortcut help
• open dialog with a grid + filterable columns
• make first column searchable
• list all keyboard shortcuts to the grid according to this list https://wiki.magnolia-cms.com/display/UX/M6+Keyboard+navigation
• group shortcuts into collapsable folders in grid
• add "cancel button" to close dialog
• add "open doc page" button to open keyboard shortcuts page in docs

Developer notes: 

• Look for lacking i18n in construction of ShortcutListeners.