Refs #2624, add INI config options that will force a new visit if campaign/website referrer information changes between actions. Includes new tracker hook shouldForceNewVisit that dimensions can use to force a new visit during tracking. Also includes light refactoring to referrer dimensions. Testless.
Removing dead code in Tracker/Visit.php.
Do not create new visit if no referrer info in current action, but referrer info present in last action. Also add integration + system tests for new behavior.
Applying review changes: remove tracker_ prefix from config names, move shouldForceNewVisit to VisitDimension and simplify triggerPredicateHookOnDimensions.
Tweak new option comments.
Fix typo in last commit.
Fixing more typos.
Merge pull request #6847 from piwik/campaign_change_new_visit

Create new visit on different campaign info or different referrer website (includes minor refactoring to Referrer dimensions + 2 new INI config options).