Preliminary support for ActiveRecord-style attribute-nesting, e.g. `form.fields_for`

Also Datamappify now requires at least ruby 2.0
Tweaked Concerns::UpdatePrimaryRecord
Do not ignore primary records, fixes the persistent issue in edge cases where the primary records don't hold any "real" attributes
Implicit "super"
Respect association's item order, also fixes a nasty gotcha in Sequel where the primary record's ID WILL BE FUCKING REPLACED by the join record's ID… *shrugs*