Move mshift.* to pbcutil/

- Remove unnecessary includes of mshift.h.
- Replace mshift.h includes in headers with forward declarations of
  t_graph where applicable.
- Add some missing mshift.h includes to source files that were getting
  it transitively from one of the above headers.
- Convert mshift.c to C++ and get rid of macros.h dependency.

Change-Id: Ie0671cd6d683f5092243e5fdcb102641fdb6ecf6