Use getPrettyNumber in all relevant parts of Piwik #3154

Piwik::getPrettyNumber, which turns 1000000 into 1,000,000 or 1.000.000 should be used on every numeric value in Piwik to make report data more readable. I think this can be done by:

• Modifying existing prettify-ing functions so they make use of Piwik::getPrettyNumber.
• Creating a generic DataTable filter that applies getPrettyNumber to metrics that have no unit (ie, visits). Would have to be applied by ViewDataTable, not the API.

Should probably be done after widget integration testing is up and running.

Sounds like a good plan! Alternatively we could do it in a Smarty filter with a regex... but hoooking in datatatable is doable too (and yes, not in the API result)

Merged in: #1254 (Nunber internationalization)