refs #5940 moved files into a subfolder framework, added autoloader to remove duplicated code to load autoload.php and to be able to register more autoloaders (eg for test files) on demand. This I got read of many includes that had to be updated all the time and that had to be updated all the time when moving iles

- renamed code coverage tests units to new structure
- removed processed system test files from git, added to .gitignore

refs #5940 we might stay backwards compatible this way for 2 months. moved some tests from unit to integration and explained when a test is a unit test, an integration test or a system test.

refs #5940 put tests in correct folders, better testsuite names, some tests still fail and I cannot figure out why

Fixes #6313 - When a user starts to get a User ID set, then we set this User ID to the existing visit rather than create a new visit for this user id specifically

coding style fixes, some PHPStorm inspection fixes, improved readability of code, few refactorings, all as part of our code cleanup strategy

User ID is NULLable now results in expected tests results: nb_users = 0 when no user id was set. refs #3490 #6162

refs #6162 when aggregating periods, do not sum 'Unique Users' metric as this is not a valid operation.

refs #6045 #6049 added an event to collect visitor info and made sure the Piwik UI kinda works when most tracker plugins are disabled

refs #5863 another try to move translations into plugins. This time we always load all translations of all plugins that are not 3rd party and bogus. As the translation file will be cached the time to load the translation drops from > 10ms to 1ms

This reverts commit 62ba8dfb.