T600 incorrect holdings

Summon does not return George Mason ids with 'm' prefix. However it does include 'b' prefix on Georgtown items. This pull request includes some logic in ui.summon to make sure the 'summon' id that is made available in search results has the 'm' prefix.

Hopefully this pull request isn't too confusing since it includes changes in #614 You'll want to decide to merge #614 or not first. If you decide not to merge #614 then we'll want to close this pull request un-merged. If you would prefer to see a pull request without #614 in it let me know.