Fix compilation warnings and errors
Fix almost all compilation warnings and errors.
Especially note the second commit. By shifting the g++ options for compiler warnings to each subdirectory of hiflow except for contrib, the warnings for contrib are disabled. This is desirable, as the code in contrib is not ought to be maintained by us.
Almost all, because there are some boost deprecation warnings that apparently cannot be fixed, because it seems like boost complains about it using its own deprecated header files.