Sub-grid data handling finished.

Note that:
the reverseRelation key from Backbone.Relational could cause a
infinit-loop in Backbone.Validations when perfroming in collection
model data 'update' so, it is now removed from model definition.

The datagrid is now working in two modes: top-level and editor. using
the parentCt.collectionRef key to distinguish the two.

The form is changed to function as a no-data-op view only to trigger
the model validations. It delegates to the datagrid to find out how to
update the data (to server or to collection first)