T600 incorrect holdings

Summon does not return George Mason ids with 'm' prefix. However it does include 'b' prefix on Georgtown items. I've updated ui.summon to adjust the 'summon' id that is made available in search results. 

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.