Changed the model space get function in the nucleus library.  Now returns all the shells
starting from the next lowest shell closure.  So for Z = 50 it will return all shells from 28 up.
For Z = 51 will return all shells up the 50 closure (so starting with 1g7/2)

Reaction manager takes the Z Model space and the N model space and looks for valid GT transitions based
on the following criteria.  The starting shell must have some occupancy and the final shell must be empty.
At the moment these occupancies are based on pure single particle level filling.  It than checks that the
transitions obeys the GT selection rules.

At present only (p,n) direction is implemented in reaction manager's FindGTTransitions method.

Added NormodFile.[cc,hh] to the repo.  Wrote a Transition Object which just holds a vector of pairs of shells
to pass between manager and other objects (right now NormodFile).