This pull request sets the logger used in the tracker to the NullLogger, unless
[Tracker] debug is set to 1.
Also includes the following changes: - There is now a dedicated tracker DI config environment. - ContainerFactory now allows plugins to have environment related config, eg, plugins/Monolog/config/tracker.php. - There are some tweaks to profiler setup so profiling results are more accurate (things like not accessing StaticContainer from within the profiler setup methods and not accessing SettingsPiwik::getPiwikUrl until after a run is done). - Also includes an update to php-di in composer.lock. Can revert if needed.
Here is a profiling run of the tracker w/ these changes: https://blackfire.io/profiles/6a5f3c65-cbf5-48c9-99d3-c28faaedb38a/graph
:+1: looks good