AbstractMarker

Added ‘AbstractMarker’ class and a vector of abstractMarker to the
tgModel class.

Abstract Markers are the non-physical entities that are attached to a
specific rigid body from a specific point. They provide exact location
of that point while the rigid body moves and rotates.

They are visualized by spheres in the graphics simulation. They are
also used to receive positions for control algorithms.
removed extra ‘;’ character.
SuperBallModel reconstructred and moveModel added

SuperBallModel is reconstructed so that it will have different
numbering for nodes. I also added helper functions and arrays to find
corresponding rods or nodes (such as what is the node that is at the
end of the same rod?)

Added moveModel function so that after the model is created, user can
manually give position, velocity and rotation to the structure. This is
necessary for controls experiments.