Move Problem Interface to problem package
Bruss2D implements Problem
MBody4h Problem implementation
Mbody with variable Body count
MBody Tests for Peer & RK looking good

Compared to the Fortran Codes using the following parameters:
BodyCount: 4
AbsoluteTolerance = RelativeTolerance = 1E-5
Integration from t0 = 0.0 to te = 0.1