ENH: Implement switching Gaussian Markov chain

The dynamics matrix switches between a set of dynamics matrices. The
switching can be done using, for instance, categorical Markov chain
(HMM).
ENH: Implement rotation speed-up for switching LSSM

bayespy.inference.vmp.transformation.RotateSwitchingMarkovChain
implements rotation speed-ups for LSSM with switching dynamics.
DEMO: Use switching dynamics in switching LSSM demo

Previously, the demo switched the whole linear state-space model. Now,
only dynamics are switched, it seems to work much better.