remove pg dependency

Currently, l2met uses PG to store librato credentials. There is a tokens table which has an uuid that is exchanged for a librato username and password. When log data comes in, the token's uuid is given in the HTTP basic auth field. We convert the uuid into the librato credentials just before we submit data to librato. @daneharrigan pointed out that this is a huge waste of time and energy. Instead, l2met users can embed the librato username and api token in the basic section of their l2met drain url. (Need to url encode the email address associated with the librato account)