Refactor: libcrmcommon: Add an easier way to register formats.

Instead of having separate steps of defining and adding command line options
and then separately having to register the formatter itself, there is now a
single pcmkregister_formats function that takes a table of new structures.
pcmkregister_format still exists and takes a lot of arguments, similar to
how pcmkregister_message and pcmkregister_messages are split up.

Note that for the moment, the GOptionContext being passed around doesn't
do anything. It's being created in stonith_admin only so everything
continues to compile. That will change soon.