Added SNS Acceleration IK Solver Interface with UnitTest

[robodreamer]

• added sns acceleration ik class and SNS_Base_Acc type
• added Jacobian dot computation
• created unit test with sawyer model
• fixed some bugs in sns_ik_acc_base and sns_ik_vel_base codes

NOTE: Acc IK solver was created as another type of Vel IK solver, I am trying to figure out a better way to do this, so any suggestions are more than welcome! But this code works and it passes unit test.