The OperationBar is a widget which offer the user the possibility to use
all the loaded operations.

EIImageService is the main GenericInterface::Service who manage the
application's specific stuff.

A PluginManager is a GenericInterface::Service which manage the loading
of plugin's libraries and the creations of OperationService instances.

A PluginService is a GenericInterface::Service which manage one Plugin.

An OperationService is a GenericInterface::Service which manage one
Operation.