Fixes according to code review feedback.
Schema change. Change the hash key to facilitate the query over health code and study key. The question is which consent document the user has consented.
Add a method to get the consent timestamp.
Add ConsentRequiredException in the dao package.
Partial implementation of the consent service.
Fix test failures.
Merge remote-tracking branch 'base/develop' into develop
Merge pull request #155 from eric-wu/develop

Misc. user consent improvements