Coding day 2015 particle properties

=Description=


 * By using the Espresso manual and the file src/python/espressomd/particle_data.pyx, check if all particle properties are implemented in Python.
 * Implement missing particle properties

=Adding particle properties DONE =
 * in src/core/particle_data.hpp, identify the part of the Particle strucutre, or its substructuires such as Particle_properties which contains the data for the relevant property
 * If the relevant members are not enclosed in #ifdefs, expose the relevant data structures in Cython in src/python/espressomd/particle_data.pxd. See ParticleProperties and ParticlePosition as examples.
 * If the member of the data structure IS enclosed in ifdefs, a workaroudn is needed. In src/core/particle_data.cpp and .hpp, write a getter function for the property. See pointer_to_dip as example. Then make this function available to cython in src/python/espressomd/particle_data.pxd (again, use poitner_to_dip as example)
 * In src/core/particle_data.cpp or .hpp, identify the setter-function for the particle property (example: set_particle_quat)
 * Finally, implement the property in Cython in src/python/espressomd/particle_data.pyx
 * For properties which are always compiled in, use the velocity as example (search for "property v:")
 * For properties which used ifdefs in the data structure, use the dipole moment as example (search for "property dip:")