Add or fix PiwikRequest.setUserCustomVariable() to put data in insertion order

[rparashchak]

Unordered user custom variables in piwik.piwik_log_visit table due to PiwikJsonObject class has field map implementation HashMap instead of LinkedHashMap.
Would you be kind enough to fix it?

[bcsorba]

Thanks for pointing this out - will be opening up an issue to increase the functionality of setting these custom variables.

[bcsorba]

Released in 1.0.1