ext/musicbrainz/gsttrm.*: Add support for using a proxy server when getting a trm id from the MusicBrainz database (#...

Original commit message from CVS:
Reviewed by:  Ronald S. Bultje  <rbultje@ronald.bitfreak.net>
* ext/musicbrainz/gsttrm.c: (gst_musicbrainz_class_init),
(gst_musicbrainz_init), (gst_musicbrainz_chain),
(gst_musicbrainz_set_property), (gst_musicbrainz_get_property):
* ext/musicbrainz/gsttrm.h:
Add support for using a proxy server when getting a trm id from
the MusicBrainz database (#149613).