Pinv velocity solver sigma output

[craigirobot]

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The main purpose of this request is to add member functions to retrieve the singular values from the pseudoinverse velocity solver. These can be used to generate manipulability feedback to the user similar to that already present in the wdls velocity solver. A function was also added to sort the singular values in descending order in order to retrieve the minimum singular value. Functions were also added for setting/getting the number of iterations and singularity threshold.