refs #3330 ranking query

 * Piwik_RankingQuery encapsulates the logic to apply the limit + grouping of others to an arbitrary select query
 * queryActionsByDimension() and queryVisitsByDimension() in Piwik_ArchiveProcessing_Day get new parameters to use the ranking query

git-svn-id: http://dev.piwik.org/svn/trunk@6803 59fd770c-687e-43c8-a1e3-f5a4ff64c105