Add CDG advection scheme

[davelee2804]

Full CDG code as branched from ocean/develop before FCT operator split merge for compatibility between advection schemes

• verified with idealized and global ocean test cases
• see submitted paper at: https://arxiv.org/pdf/1711.04928.pdf
• adding Andrew Bradley's SIQK c++ polygon intersection code to operators/ (in framework) and linking to c++ library in top level Makefile
• package and control parameter calls added to core_interface and forward_mode routines
• adding Bill Lipscombs projection operators to operators (in framework)
• reverted removal of vertical monotonicity limiting in the FCT transport code