Factorize ConstraintSolvers

[hugtalbot]

Today, SOFA proposes two ConstraintSolvers:

• LCPConstraintSolver
• GenericConstraintSolvers

Both solve a constraint problem (LCP or NCLP). Therefore, here are some todo suggestions:

• implementations should be merged, triggering the optimization for UnilateralInteractionConstraint of the LCPConstraintSolver when the problem only involves such constraints
• a unique component with a clear/simple name (ConstraintSolver) should be used
• the solver used should be a dedicated component in the scene : different methods to solve such a problem could be used, #3053 introduced a NNGS on top of the GaussSeidel (double implementation in LCPConstraintSolver & GenericConstraintSolvers) they should be extracted as components

Possibly interested people: @courtecuisse @ChristianDuriez @alxbilger @EulalieCoevoet @Younesssss