The great C function dependency refactor of 2020

The goal of this commit is that: only modules that either are part-of sbbs.dll/libsbbs.so or need to link with/use that library, will #include "sbbs.h" and thus be dependent on its subsequent includes (e.g. cryptlib.h, jsapi.h). This should mean extdeps.mk can be trimmed way down.

I also removed CVS keyword/comments and trimmed up the boilerplate copyright notice in modified and added source/header files in this commit.

There is no functional change in behavior in this comment.