implement hypervisor mode from double-tap-restore

[Ben-401]

currently a hook/handler has been implemented to:

• detect when a double-tap restore-key is made
• enter HYP-mode
• change border color (*)
• leave HYP-mode

It is expected that the functionality at (*) be developed to:

• display a menu on the screen
• provide HYP-mode functionality
• allow clean exit from HYP-mode

[gardners]

Some work has been done on this. Note that double-tap RESTORE is now "hold RESTORE for 0.5 - 1 second" (2 - 4 seconds still does reset, and <0.5 seconds, triggers NMI as normal).