Added 4-particle vecangle potential; untested, and configuration.cpp still needs to build the potential dictionary using type,filename tuples as keys

Changed BondAngle to be the product of the energy of potentials applied to the central bond and two angles formed by four particles

Fix crashes caused by unneccesary updateParticleList call prior to RB attached particle update and improper initialization of atomic indicies for RB attached particles

Ensure 'particle' or 'rigidbody' keywords found in .bd file before processing subkeywords; move grid boundary condition into BrownianParitcleType; use constexpr instead of #define in a few spots