Refactored Piwik\Translate into a non-static class Piwik\Translation\Translator
Added a PHPUnit group for the Translation component
Moved loading of plugin translations from Plugin Manager to Translator
Removed all usages of $GLOBALS for the translations
Variable renaming
Fixed small bug
Refactored the way translations are loaded

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.
Fix unit tests by loading no translations by default in tests
Removed useless translations loading (now lazily-loaded)
Fixed typo that crept in
Removed useless import
Use branch for CustomAlerts plugin
Use branch for CustomAlerts plugin
Fix tests for CSV export
Moved `Piwik\Translate\Writer` and its subclasses to the LanguagesManager plugin

These classes are only used in that plugin, so it doesn't make sense to keep then in Core.
Added a `StaticContainer::get()` method to avoid boilerplate
Created data provider classes in a new Intl component

Less code in `Piwik\Common`, less static classes, more isolated components.
Use data providers instead of including data files