Enable the SIP server to speak UTF8 or ASCII, defaulting to ASCII

Enable the SIP server to speak UTF8 or ASCII, defaulting to ASCII

Some SIP clients have implemented UTF8 support, and it is desirable to
avoid mangling non-ASCII characters when possible, so a new <encoding>
option in the SIPServer config file enables sites to specify an
alternate encoding (such as "utf8"). The example oils_sip.xml file
will continue to default to ASCII, and if no <encoding> option is
supplied in the config file, ASCII will be the default.

In addition, this patch improves the ASCII option by applying the
ASCII mangling to all text fields, as well as ensuring that the
incoming data is in Normalization Form D mode to make the mangling
work cleanly.

Other encodings such as iso-8859-1 can be specified, but to properly
handle other encodings a transliteration phase would have to be added
to the OpenILS::SIP::clean_text()...

git-svn-id: svn://svn.open-ils.org/ILS/trunk@15260 dcc99617-32d9-48b4-a31d-7c20da2025e4