Merge pull request #261 from atlasapi/mbst-5412-image-urls

Switch image attribute back to using legacy scheme for PA
Equiv sequence scoring null for top-level series parent mismatch

When scoring two episodes by sequence either both must have a top-level
series as parent or neither, otherwise the score is null. Episodes in a
standard Brand/Series/Episode hierarchy will score null against an
Episode in a Series/Episode hierarchy.

Detection of Episodes as children of top-level Series is through
checking the episode's parent ref is the same as its series ref.
Merge branch 'mbst-5333-equiv-top-level-seq' into stage

* mbst-5333-equiv-top-level-seq:
  Equiv sequence scoring null for top-level series parent mismatch