Allow Segments to define multiple SQL columns if the segment value can be matched in any of those fields, and use to define two new segments: customVariableName & customVariableValue.

Add integration test for ArchiveTableDao class and system test for new analyze archive table command.

Fix function signature in VisitRequestProcessor and move tests in VisitTest regarding isVisitNew to new test case for VisitRequestProcessor.

Move bulk of logic in Visitor class to new stateless service, VisitorRecognizer which is stored in DI. Also fix two integration tests.

Display a meaningful & useful error message when setting viewDataTable parameters, rather than silently fail

eg. https://travis-ci.org/piwik/piwik/jobs/68411560

Adding server side logic for ping requests that specify a visit is still ongoing, w/o creating a new action. Includes a new integration test for the feature.