Refactoring

- add an expired Timestamp to simplify logic
- Switch to UTC timestamps
- switch to minutes rather than days for expiration.
  Easier to test
- move all DB code to sqlite3db.go
- remove global db reference
- pass db ref into handler via a struct and pass handler into negroni
- extract DB sql strings into constants
- extract Gensendgorow into it's own file
 - add helpers for String() and rows Scan()