Extend tracking with all changes.
Merge pull request #6380 from czolnowski/extend-tracking-code-clean

Let plugins further extend tracking code via Event 'Piwik.getJavascriptCode'
Remove token auth option from core:run-scheduled-tasks command since superuser access now allowed for all commands.
Remove unnecessary UITests testsuite in phpunit.xml.dist file.
Add setSingletonInstance method to Option for testing.
add @ignore so the method does not appear in the auto generated API doc on http://developer.piwik.org/api-reference/classes
Increasing PHP requirements to 5.3.3 refs #6390
Merge branch 'master' into deprecate_usersettings