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.

Refs #5800, add namespaces to integration tests in root folder. Also add IntegrationTestCase to a namespace, re-add individual test @groups, move test groups to class level, and rename test files & class names so underscores are not used.

If a dimension only implements a getName() method it should extend Dimension and not VisitDimension which is more "correct" and improves performance since we do not have to check whether they are installed and whether they implement certain methods

this is epic... by rendering the reports this way we can remove a lot of duplicated, unneeded code while having backwards compatible urls, developers are still able to completely overwrite the reports controller action, we fix some issues where CoreHome.renderWidget was reported in dispatch events instead of the actual module/action -> fixes also some security issues and most saved params for reports work again. Hope it works as expected

moved some more dimensions to plugins, fixed some issues, removed some more duplicated code etc. Tests will not be green as there fixes to country detection

as the category is used for reportMetadata and widgetsList we should not translate the category. The reportMetadata wants it translated but widgetslist wants the translation key. So we translate it only for the reportMetadata. Best solution would be to always accept either translated or the key but one problem after another