Numerical integrator for collocation BEM

[robertodr]

Provide a numerical integrator for the collocation BEM.

Possible Solution

There is some, mildly tested, code for this functionality already in Numerical.hpp](https://github.com/PCMSolver/pcmsolver/blob/release/1.Y/src/bi_operators/Numerical.hpp) and [Numerical.cpp
It needs additional testing, possibly against GAMESS.