Fixed several bugs related to evidence. Hopefully included LinearBeta, still needs testing though. Changed sample_global and sample_local once again in ContinuousNode

examples/MCMC_Continuous.py läuft mit exponentialverteilung->linearGauss, Evidenz als Klassen und Kontinuierliche PoE läuft

Refactoring: ContinuousNode introduced, moved stuff from Discrete and Continuous Node so generic Node, created MCMC example for multiple continuous Models

Contstructing a MarkovChain with MetropolisHastings is now working for Networks which consist only of LinearGaussian nodes or ProbabilityTables. Additionally it is now possible to specify the form of densityfunction that one expects for PosteriorMarginal. Learning a Gaussian from a MarkovChain is also possible

ExampleComparison is running correctly, Added MetropolisHastingsAlgorithm as StateTransition and began generalization of MCMC to continuous spaces