Fixed redis connections closing prematurely

Modified redisView in db.js to close redis connections with `client.quit()` instead of `client.end()`, since that is [what the documentation recommends](https://github.com/mranney/node_redis#clientend). This avoids prematurely closing the connection if a request is still awaiting a reply.

Also fixed the POST submit endpoint to close the redis connection on success.

r? @cvan @soedar @at-kevinlau