LP1829567 Angular access key improvements

LP1829567 Angular access key improvements

1. Adds support for shift+ shortcuts.
2. Remove duplicate key assignments made within the same context.  This
   is especially useful in the navigation bar since some commands repeat
   from different menus.
3. Indicate in the key assignemnts help page when an assignemnt has be
   superseded by another assignment.
4. Open the help page in large-dialog mode for more room.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>