Added more skeleton code and filled some routines

Added ScatMatType, XSMeshType.  Filled in code for initExtSource_P0,
computeMGFS_P0, updateInScatter_P0.  Added declarations for expoa,
expob; both are unallocated for now.  Added initExtSource method
to SourceType and SourceType_P0.  Added rsinpolang to AngQuadType.
More additions/improvements to sweeper.f90

Added hasSource, pz, qext, XSMesh members to sweeperType.  Removed
a couple problematic attributes from longRayDat and phiang.  Added
setExtSource procedure pointer and corrected a typo in name of
absintfc_sweep.

Added setExtSource_MOCP0 and MOCSolver_Setup1GFSP routines.  Changed
name of sweepP0_1G routine to MOCSolver_Sweep1G to match MPACT.