Feature/ik panda

[Joobz]

This PR changes and adds some functions in kinematics:

• poseGoalObjectives(): add prior to link COM poses.
• jointAngleObjectives(): modified it so we can add any mean to the prior. Previously it was always centered at the origin.
• jointAngleLimits(): add a jointLimitFactor only to the angles, compared to the one in joints that adds a factor to all dynamics related variables.
• initialValues(): modified it so we can start from non-random points for arbitrary joints.
• inverseWithPose(): IK with a given COM pose for the 7th link.

There are also some changes to Robot and Joint files that @dellaert changed because we ran into some problems.

[varunagrawal]

@Joobz please finish up this PR before you head out, else it will stay in review purgatory. :)