{Reviewer: Mike} Allow initial Filter Criteria to specify SIP header matches

Mike, can you review? astyle has made several indentation changes in pjutils.cpp, which is annoying, but my only actual change there is the addition of std::string PJUtils::get_header_value(pjsip_hdr* header) .

I haven't live-tested yet, but my UTs are fairly extensive, so this should be safe to review.