Add update submission function to submission_repo

[jcadam14]

Need to add an update submission function to the submission_repo. Right now, it only has an add function. The update will need to create a session, start the transaction, merge the incoming DAO, and close the transaction and session. Finally, return the merged object.

Current behavior

No update function in the repo

Expected behavior

DAO that is being passed around to validation can be updated with state changes and saved to the DB