[pmc] moved implementation of [Cor+12] to separate class

o introduced class DeterministicIS
o next step: rewrite pmc.py
[pmc/proposal] bugfix in class MixtureProposal

o wrong distribution of samples to member-components
[pmc] implemented support for tracing samples

o MixtureProposals can now return an array which contains the number
  of the responsible component for each sample
o ImportanceSamplers can now return that array along with the run method