Lazy loading DAO members

[almgong]

It is much faster to lazy load DAO members, such as initializing the set of Proteins associated with a given Gene, compared to implementing a standalone method that retrieves the result set manually.

Ideally, there should be methods to initialize individual lazy loaded members, and a general "load-all" method that loads all lazy loaded members. This is because some DAO classes can have multiple llm's but not all are needed at any given time (e.g. some applications just need the set of Diseases given a Gene, and not the DiseaseGene relationships).