Append X10 event fragments rendered to URL string only if not null to avoid "null" in event fragments.
Removed data sorting to retain original order, otherwise event's category/action/label is mixed up.
Set request's User-Agent from visitor if one is provided.
Added utmvid (Unique visitor ID) parameter support so GA can recognize returning visitors.
Merge pull request #1 from goshki/master

Event and User-Agent reporting fixes, utmvid parameter support, null values control.