CartoDB-SQL-API metrics

Timers

sqlapi.query: time to return a query resultset from the API, splitted into:
- sqlapi.query.init: time to prepare params from the request
- sqlapi.query.getDBParams: time to retrieve the database connection params
- sqlapi.query.authenticate: time to determine if request is authenticated
- sqlapi.query.setDBAuth: time to set the authenticated connection params
- sqlapi.query.queryExplain: time to retrieve affected tables from the query
- sqlapi.query.eventedQuery: (pg) Time to prepare and execute the query
- sqlapi.query.beforeSink: time to start sending the response.
- sqlapi.query.gotRows: Time until it finished processing all rows in the resultset.
- sqlapi.query.generate: Time to prepare and generate a response from ogr
- sqlapi.query.finish: time to handle an exception