Archive.php memory improvements (up to 10 times less memory required!)

[mattab]

At InnoCraft we are running Piwik for large and very large websites and have identified challenges in memory usage during pre-processing of report data.

The goal of this ticket is to investigate with XHProf profiler, and find the cause of these memory issues and fix them.

Archiving memory required before investigation started: 8Gb.

Memory after the ticket is implemented: 1Gb.

THE POWER OF BETTER CODE. NO LEAK.

[mattab]

Call Table\Manager::deleteAll() for both Days and Periods, not only for Periods

in 1948b75

[mattab]

should use less memory when aggregating data table records in dc2d18d