Support members for group artists, other than specifying their roles
Properly (ish) collapse multiple member relationships into one for JSON-LD.
List roles for artists as best I can.
Include release groups in artist json-ld markup.
Merge branch 'json-ld-20141205' into beta

* json-ld-20141205:
  Include release groups in artist json-ld markup.
  List roles for artists as best I can.
  Properly (ish) collapse multiple member relationships into one for JSON-LD.
  Support members for group artists, other than specifying their roles