Add a new potential MWPotential2014

configure.ac

doc/RTD/source/ExternalPotentials/index.rst

examples/GravityTests/Hernquist_circularorbit/makeIC.py

examples/GravityTests/MWPotential2014_circularorbit/README

...ples/GravityTests/MWPotential2014_circularorbit/makeIC.py

...s/GravityTests/MWPotential2014_circularorbit/makePlots.py

...ityTests/MWPotential2014_circularorbit/original_radii.txt

...vityTests/MWPotential2014_circularorbit/params_unit_1.yml

...vityTests/MWPotential2014_circularorbit/params_unit_2.yml

examples/GravityTests/MWPotential2014_circularorbit/run.sh

examples/parameter_example.yml

src/potential.h

src/potential/MWPotential2014/potential.h