EUCA-7189
Added to ui-subset - additions/removals to 'selected' now trigger the opposite reaction in 'available'. The result is that selected options don't appear in the selection list, unless you change your mind and remove them again.

EUCA-7220
Found models/zone.js duplicating models/availabilityzone.js, but not setting the ID properly and was being treated as a separate entity by dataholder. Removed it and its collection, and fixed a few places in the codebase that used it.
Merge branch 'EUCA-7189' into maint/3.3/testing