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.

Make CustomVariableName/CustomVariableValue derive from VisitDimension instead of Dimension so we can define segments in them.

Refactor API.getSegmentsMetadata and Plugin\Segment so segments are all defined through Plugin\Segment class in dimensions & make sure AutoSuggestAPITest data providers do not use database.

Move CustomVariables tracking logic to CustomVariablesRequestProcessor. Includes two methods in RequestProcessor, onNewVisit and onExistingVisit (matches Dimension methods).

Imporves performance for Archiving and Range dates. Makes all kind of
reports faster as well. Fixed bugs in labelFilter, reports total calculation
and more.

Also replaceColumnNames is now queued again which should bring
a performance boost in general.

fixes https://github.com/piwik/piwik/issues/7184

Fixes #3147 Add rel="noreferrer" to all outgoing links . This works in Firefox so far and only for "left clicks". Not perfect, but hopefully other browsers will implement this in the future, as it's a useful privacy enhancing feature!