Added default value information for comments.
Added GNU Scientific Library.
The GNU Scientific Library (GSL) has been added to the list of
libraries. It might be useful to carry out certain mathematical
operations.
slipPlane.cpp: Cleaned up defect access in
SlipPlane::moveDislocationsToLocalEquilibrium.

grainboundary.h: Added default values for all arguments.
GrainBoundary constructor: Added base as argument to Defect conctructor
call.