Added third partials for residual Helmholtz energy for SAFT term and passing Catch tests.  Type 1 and Type 2B associating fluids are now more similar (derived from common base class, set a single flag in base class).

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Updated ipython notebook for associating fluids

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>