Translations aboard !

Now the plugin is fully translatable...

Added

• Call translation on all labels, plugin is translation ready !
• Add a new function wpmautic_get_tracking_attributes which defines attributes to be sent through JS and Image trackers.
• Add a filter wpmautic_tracking_attributes to allow developers injecting custom attributes in trackers.
• Add the ability to track logged user (within an option)

Changed

• Add valid text domain and start official translation process.