Refactor: libcrmcommon: New pcmk__html_set_title()

As mentioned in other comments, a title really should be set per output
object, not as a file-scope variable. However, this will work for now.
We're continuing to use the file-scope variable until we find a better
way to do per-format command line argument parsing.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>