Merge pull request #4834 from RosettaCommons/roccomoretti/iosfwd
Convert stream header usage to iosfwd
As the templated stream headers can be rather bulky, the C++ standard library provides an iosfwd header to forward declare many of the classes & objects which are provided by them. By using the iosfwd header instead of something like iostream in the hh files, we can possibly simplify & speed up compiles, by not forcing the compiler to include/compile the stream headers when they're not needed.
Most of this was an automated replacement of includes in header files, followed by a "will it compile" fixup. There were some movement of functions to cc files, and some conversions of izstream and ozstream to plain std::istream and std::ostream in function signatures. (You can pass an ozstream to a std::ostream reference.)