Load testing Script helper: copy visits/pages/conversions from custom date range to today #2626

Copying old logs with server_time = CURRENT_DATE() means we can try Piwik in a "production" like environment. Running the script to copy the last week of data, into today, will effectively generate an unusual load on Piwik.

This script will allow to quickly generate huge piwik logs from a starting database (even with old data).

Script only used by developers

(In [5106]) Fixes #2626

• Adding new script that will copy old visits/actions/conversions/purchased items from a date range (start,end) in TODAY. This is useful script to test the recent archive.php optimizations on a lot of data.
  The only downside of this technique is that we effectively copy old data, therefore a few things are not as "varied" as they would be in prod, such as: Page URLs distribution (we "reuse" past URLs when normal piwik would always track new ones)

I'm hoping to extend it later to generate this huge load over multiple days, as well as generating over a given number of websites.