Allow queries on 1:N tables

Initial work to support unlimited number of joins for existing
and future data sets.  Previously could only query the primary
and secondary table, which did not conform to the UI data schema.
Consolidate and provide interface for uploadables

Further abstracting the loading process to be shared by different
parts of the code
Uploadables for Reac, Parcel, Real Property and Subsidy
Reduce nesting in query loop

Minor code cleanup
Merge pull request #37 from azavea/topic/additional-uploads

Topic/additional uploads