Make printing of SVG files optional in mondriaanOpt

docs/USERS_GUIDE_OPT.html

src/MondriaanOpt/MondriaanOpt.c

src/MondriaanOpt/errors.c

src/MondriaanOpt/options.c

src/MondriaanOpt/options.h

src/MondriaanOpt/solution.c

src/MondriaanOpt/solution.h

src/MondriaanOpt/solver.c