Added different potentials

 - Added ELRAD.dat file, which is the same as ELNAME.dat, but with an
extra column that includes the element radius
- functions.h: cleaned up
- ion.cc: Fixed prep_FF bug. Added enum for ion type
- mytrim_range.cc: Fixed prep_FF bug
- simconf.cc: Added data pull for elemental radius
- trim.cc: cleaned up fullTraj display. Added calcS2 method to
determine sin^2(theta/2) for different potentials. Added support for
potentials NONE, HARDSPHERE, RUTHERFORD, and TRIM.