Add new RequestProcessor to Actions plugin for action detection + new RequestProcessor for ping request handling. Ping request handling is performed in new Heartbeat plugin. Also added a new method to Plugin, isTrackerPlugin for plugins to override if they are tracker plugins, but don't have a dimension or implement a tracker method.

refs #8304 make sure to not uninstall a dimension if another plugin defines the same, make sure to correctly mark the dimension as uninstalled

Fixes #8110, make sure plugins are sorted correctly during tests. Moved plugin sorting logic from Plugin\Manager to PluginList.

The plugin is used for clearing the caches, so it needs to be unloaded after.

As the plugin does now nothing anymore, I removed it.

Fix translation edit in last commit and remove local config check in FrontController since it's done by EnvironmentValidator.

Added environment validation system test (mostly failing) that tests Piwik's behavior when INI files are gone or corrupt from each Piwik endpoint (tracker/reporting UI/console). Hacked test code to make it possible and for some tests to pass.

Documenting new classes + removing PluginList::getInstalledPlugins method since it is not required for this PR.

Remove uses of Config::init(), Config::clear() and Config::setTestEnvironment(). Replace last w/ mock config class, which is closer to use of DI.

Rename UpdateListener to UpdateObserver and use in CLI update command to show progress of update. Also remove CLI output code from CoreUpdater\Controller::runUpdaterAndExit.

Hide error when reading the Plugins array, when this function is called before we have a config.ini.php file
fixes https://github.com/PiwikPRO/plugin-EnterpriseAdmin/issues/31

Translations are now lazily loaded instead of being explicitely loaded by other components (e.g. the front controller, the plugin manager, etc...). Now other parties only configure "directories" where the translator can find translations. That makes the translator decoupled from the rest of Piwik.

The "verbose" level doesn't exist in PSR-3, the lowest one is "debug".

Fixes #6529 before loading plugins in memory, order the list the same as it is in global.ini.php  - then load remaining plugins in alphabetical order

try to remove version option in case we are uninstalling a dimension and remove a log_conversion column in a VisitDimension only if it implements a conversion

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

refs #6065 remove tracker plugins from config and cache them instead in a file. Wondering which test will fail...

refs #5863 we need to pass the langCode to loadPluginTranslations() otherwise langCode will be always an empty string. If there is no plugin loaded yet and no language generate a simple cache file for core translations, load a translation only if a langCode is there