Fix schema.org mapping for MusicAlbum, add Map

We had set LDR[06] = j to MusicRecording, but that is really meant for
individual songs. Use MusicAlbum instead, and per
http://schema.org/MusicAlbum, use a new MusicGroup itemtype with a
'byArtist' property for the primary artist rather than the generic
'accountablePerson'.

Also map LDR[06] = e to Map, because that seems like a safe bet.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Mike Rylander <mrylander@gmail.com>

Conflicts:
	Open-ILS/src/templates/opac/parts/record/authors.tt2