fixes #6123 tooltip was not formatted correct
Merge branch 'master' of github.com:piwik/piwik
Fix for bd7dc4d60 which broke the build (null bytes where not sanitized)
refs #6432 should prevent possible TypeError

I was not able to reproduce this issue but also noticed there could
be an issue under circumstances. Need to know the exact steps to
reproduce
Extracted `Piwik::getJavascriptCode()` into a separate, non static class: `Piwik\Tracker\TrackerCodeGenerator`

`Piwik::getJavascriptCode()` is now deprecated in favor of the new class.