add expectation propagation inference method
Merge pull request #1462 from votjakovr/feature/gp_binary_classification

Add expectation propagation inference method
Remove double sudo in travis octave 3.6 second ppa.
Remove octave 3.6 second ppa in travis.
add expectation propagation to modular interfaces
Merge pull request #1463 from votjakovr/feature/gp_binary_classification

Add expectation propagation to modular interfaces