An attempt at flexible attributes with plugin namespaces.
Mostly untested.
Started hacking `CollectionQuery` to search flexible attribute fields.
Fixed up a couple of query classes for flex attr support.
ironing out some kinks
Code for reading attributes from concatenated flex columns into dicts moved to an outside methods to make it usable for both BaseAlbum and Item objects.
Merge pull request #208 from steinitzu/flexattr

partial flexattrs