Add hydra-dialog

Adding this as a further piece of the key binding documentation, and because I want to know if I should raise an issue about the key codes being sent to text grids being off... didn't know if there is already a plan to replace/rewrite textgrids or if I should open an issue. (basically, no shift, and special keys (keypad, page up, etc.) either set t.key to an odd character or in the case of the keypad, to the underlying character with no indication that it came from the keypad.)