Merge branch '3.x-dev' into new_submoduels

CHANGELOG.md

composer.json

composer.lock

config/global.ini.php

core/API/DocumentationGenerator.php

core/Http.php

core/Notification.php

core/Plugin.php

core/Plugin/ControllerAdmin.php

core/Plugin/Dependency.php

core/Plugin/Manager.php

core/Plugin/MetadataLoader.php

core/Plugin/ReleaseChannels.php

core/ProxyHttp.php

core/SettingsPiwik.php

core/Tracker/Action.php

core/Tracker/ActionPageview.php

core/Twig.php

core/UpdateCheck.php

core/UpdateCheck/ReleaseChannel.php