begin adding v2 api

[warriorstar-orion]

This PR creates a v2 API namespace for Parastats, and adds its first method.

Besides any new API endpoints not present on v1, the v2 namespace is differentiated because it returns JSON-formatted results of feedback data, rather than a stringified JSON value.

/v2/stats/feedback:

• accepts a feedback key key_name, and two dates, start_date and end_date, which must consist of a span of two months max.
• returns a list of objects which provide a round ID and the data of the feedback for that round's key_name.

This makes it painless to quickly perform queries on individual feedback keys and helps to lessen the need for mirroring feedback data locally:

The LINQ query resolves nicely into a single SQL query which runs quickly. Concatenating the strings together the way we're doing here is a tiny bit slower, but not egregiously so for queries limited to two months max.

[warriorstar-orion]

this manages to resolve to a single query, including the substring manip, which is pretty cool:

SELECT `r`.`id`, 
       SUBSTRING(`f`.`json`, 1 + 1, CHAR_LENGTH(`f`.`json`))
FROM `feedback` AS `f`
INNER JOIN `round` AS `r` 
    ON `f`.`round_id` = `r`.`id`
WHERE (((`f`.`key_name` = @__key_name_0) 
        AND `r`.`shutdown_datetime` IS NOT NULL) 
        AND (`r`.`initialize_datetime` >= @__start_datetime_1)) 
        AND (`r`.`initialize_datetime` <= @__end_datetime_2)
ORDER BY `r`.`id`

[AffectedArc07]

I hate that we are manually constructing JSON but this PR has been up long enough.