Backend: Introduce a Collection Tree

[d-callan]

We've discussed collection variables at some length. previously we've agreed to introduce two tables to the schema:

CREATE TABLE &1.Collection ( collection_id NUMBER(10) NOT NULL, stable_id varchar2(50), description varchar2(4000), display_range_min number(10), display_range_max number(10), PRIMARY KEY (collection_id), CONSTRAINT unique_stable_id UNIQUE (stable_id));

CREATE TABLE &1.CollectionAttribute ( collection_attribute_id NUMBER(10) NOT NULL, collection_id number(10), attribute_stable_id varchar2(50), PRIMARY KEY (collection_attribute_id));

and then from these tables building a 'collections tree' similar to the existing variables tree. think things like display ranges when they exist for the collection should probably override the corresponding child variables display range. also remember talking about how parents for collections should be inferred based on the last common ancestor of the collections children.