Added max_maneuver_velocity to ship definition and ShipInfo object
WIP thruster limiter to maintain constant speed to be used in maneuver mode.
Thruster limiter is fully functional
Limit set speed mode to maximum maneuver speed
Added new string constants for: maneuver, transit, and jump modes
Preparation for maneuver mode: fixed speed control mode is now the default
Removed CONTROL_FIXHEADING_FORWARD and BACKWARD
Replaced fixed speed mode with maneuver control
Added new flight system buttons in UI replacing old flight controls

Autopilot and Maneuver mode are operational.
Merge branch 'master' into paragon_flightsystem
Fixed issue with ships that have no default max maneuver speed in ship definition. Fallback max speed is now set to the speed of light.
Autopilot button now enables/disables itself based on navigation/combat target availability.

Targeting a destination then enabling autopilot executes a fly to vicinity command.
Refinement to transit states implementation.

Start transit speed now scales with max maneuver speed so that ships having less than 100000 max maneuver speed can still transit
Fixed problem with transit sound not playing sometimes

Fixed problem with transit state not being reset when autopilot transit is interrupted
Merge branch 'master' into paragon_flightsystem
fixed docking status not activated sometimes
Fixed some transit issues
Merge branch 'master' into paragon_flightsystem
Ship slows down to max maneuver speed if transit drive is interrupted
Replaced hyperspace button with jump button for new flight system