Add a TT helper to encode email headers in UTF-8

Add a TT helper to encode email headers in UTF-8

This can and should be used to encode any headers (To, From, Subject, etc)
in an email that might include text outside of the ASCII 7-bit range. Names
of people or libraries, for example, that might otherwise come out garbled.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@19546 dcc99617-32d9-48b4-a31d-7c20da2025e4