Implement Store Handler

- Store passwords in the DB and return a token/url which can be sent to
other users to retrieve their password.
- Refactor error handling to return JSON objects as response rather than
strings
- rename urlGenerator -> UrlGenerator
- add storeNewToken to Gensendgo DAO
- validate JSONRequest on store - minimal
- fix potential UTC bug in expiresTs
- add missing error handling in dbTestDataInner