Prefix sample names with study id

Fixes #523 

On MetadataTemplate creation, it modifies the sample names to be prefixed with the study id.
Changes the PK of required sample info from `(sample_id, study_id)` to `sample_id`
Updates all the FK to be only the `sample_id`
Modifies all the code related to these changes on the DB.
(int,str) only now.