Ambigous datetime values are accepted but should be rejected

[philvarner]

These two datetime values are accepted for query, but are not valid RFC 3339 datetimes, and should be rejected with a 400.

• Search with datetime=1937-01-01T12:00:27.87+0100 returned status code 200 instead of 400 -- no colon between hour and minute in tz
• Search with datetime=1985-12-12T23:20:50.52 returned status code 200 instead of 400 -- no timezone

[geospatial-jeff]

Closed with #368