Factor out FollowingMode and DynamicsShape

Re-used FollowingMode, DynamicsShape by putting it from the Actions
itself one nesting level higher; restructured the whole message for
more clarity; clarified the description for the bool follow in
LongitudinalDistanceAction and LateralDistanceAction

Signed-off-by: Clemens Habedank <clements.habedank@partner.bmw.de>

Author: Clemens Habedank