StiffSpringForceField
---------------------

Context: Sofa.Component.SolidMechanics.Spring

Stiff springs for implicit integration

Data:
 - name : object name
 - printLog : if true, emits extra messages at runtime.
 - tags : list of the subsets the objet belongs to
 - bbox : this object bounding box
 - componentState : The state of the component among (Dirty, Valid, Undefined, Loading, Invalid).
 - listening : if true, handle the events, otherwise ignore the events
 - isCompliance : Consider the component as a compliance, else as a stiffness
 - rayleighStiffness : Rayleigh damping - stiffness matrix coefficient
 - stiffness : uniform stiffness for the all springs
 - damping : uniform damping for the all springs
 - showArrowSize : size of the axis
 - drawMode : The way springs will be drawn:
- 0: Line
- 1:Cylinder
- 2: Arrow
 - spring : pairs of indices, stiffness, damping, rest length
 - springsIndices1 : List of indices in springs from the first mstate
 - springsIndices2 : List of indices in springs from the second mstate
 - indices1 : Indices of the source points on the first model
 - indices2 : Indices of the fixed points on the second model
 - lengths : List of lengths to create the springs. Must have the same than indices1 & indices2, or if only one element, it will be applied to all springs. If empty, 0 will be applied everywhere

Links:
 - context : Graph Node containing this object (or BaseContext::getDefault() if no graph is used
 - slaves : Sub-objects used internally by this object
 - master : nullptr for regular objects, or master object for which this object is one sub-objects
 - mechanicalStates : List of mechanical states to which this component is associated
 - object1 : First object associated to this component
 - object2 : Second object associated to this component