Action datatables should use integer indexes rather than string indexes (smaller size and faster access)

[mattab]

Currently datatables for Actions are indexed with the metrics string (nb_visits, nb_hits, etc.). See code in plugins/Actions/Actions.php archiveDay()

Other datatables are using integer indexes, mapping is defined in Piwik_Archive::$mappingFromIdToName

Actions datatable should use a similar integer mapping to reduce size of Actions datatables, and make querying faster.

[mattab]

thanks to halfdan run of xhprof, we now know that this is indeed very costly, lets fix it

[mattab]

(In [3696]) Page titles report improvements fixes #1898

• new fields in 2 log tables (major schema upgrade in next release!)
• code refactored and optimized, (only the UI to display top entry/exit page titles is missing)

Performance improvements

• Actions Archiving is much more efficient, removed many JOINs and updating algorithm so that we select and parse action names only once per action.
• Fixes #1600: datatables now indexed by int, no data migration but code works with both old and new data structure
• Fixes #1780: new index

Improvements to integration tests

• never loads the Provider plugin in proxy-piwik.php since reverse ip lookup slows up tests a lot
• fixing a test result that were previously incorrect (_withCookieSupport) because a static cache wasn't cleaned after each test