Study update, exp/spec generation, DB funcs

+ Added set_study_id. Gets id from name and data group
database.py:
+ get_study_id(name, data_group)
+ get_experiments(study_id)
+ get_specimens(exp_id)

Experiment model:
+ Generates new experiments on Study post_save

Specimen model:
+ Generates new specimens on Experiment post_save