clean up the gaussian filtering notation in ch 8

[murphyk]

• rename LinGaussPredict to GaussMoments, LinearizedPredict to LinearizedMoments, and UnscentedPredict to UnscentedMoments.
• Eliminate unnecessary LinGaussUpdate function from algorithm 7, and rewrite algorithm 8 (KF) accordingly.
• Eliminate unnecessary CondLinearizedPredict function in algo 18.
• Add pseudocode for (iterated) conditional moment gaussian smoother. This changes the algorithm numbering within sec 8.7.7, but the rest of the numbering (equations, sections, etc) is unaffected. (Of course, page numbers have changed, too.)