refs #6257 visitorUUID equal by default for each new Piwik.Tracker
refs #6257 Piwik.getVisitorId() function
refs #6257 getVisitorId() unit tests
refs #6257 removed getVisitorId() from Piwik API
Merge pull request #6258 from a4tunado/6257

refs #6257 visitorUUID equal by default for each new Piwik.Tracker