Rbm/insert field halos

[rbmetcalf]

@jwhsueh Here is the modification we talked about. The new function is below. I have not done much testing of it yet so you might want to make some images to make sure nothing is going radically wrong, but I don't think so.

''' /* \brief Insert a list of field halos.

• Unlike a main halo, these halos will be put into a tree structure within each plane
• potentially making the ray-shooting faster. No background density will be subtracted
• so the light cone will always have more than the average density if mass is not subtracted
• in some other way. The redshifts of the planes are input and the halos are placed on the clossest
• plane to them in angular size distance. The redhsift and angular position of each halos must be set.

• / void Lens::InsertFieldHalos( std::vector<LensHalo > &inhalos /// list of pointers to LensHalos to be added ,const std::vector &plane_redshifts /// redshifts of planes ,bool verbose ); '''

[rbmetcalf]

I think this is working well enough to be merged.