Moved IsPlanar handling to Steering

- Steering will now handle the case of planar vehicles itself. That way
  we don't have either clear it twice (for normal and post-processor
  steerings) nor do we run into a case where the behavior disregards it.
- Removed redundant force clamping.
New Vehicle.DeltaTime property, in case a steering behavior needs it
SteerForWander is no longer framerate-dependent, changed smoothing
New property drawer for angles stored as a cosine

- Using new property drawer on SteerForNeighborGroup.
- Removed SteerForNeighborGroupEditor.
- Removed old editors for Alignment, Cohesion, Separation. They were no
  longer relevant since I did SteerForNeighborGroup.
MAJOR CHANGE: Replaced IsPlanar with AllowedMovementAxes

- We can now limit movement on any arbitrary axis, not only the Y.
- TickedVehicle.ApplySteeringForce is now the gatekeeper for the allowed
  axes.
- New Vector3Toggle property, attributes.
- Renamed DesiredSpeed to TargetSpeed for clarity, that way it's clear
  that it's not a function of DesiredVelocity.