Client changes
The client was refactored to be cleaner, in a developper point of view. Plugin management has moved from Client to Plugin Loader, which was renamed Plugin Manager (this is much more consistent).
Window Manager
A WindowManager interface and a DefaultWindowManager class implementing it were added. This will allow a fine management of opened window, by plugin, by name, ...
All plugin now creates ManagedWindows instead of JFrames. The behaviour is unchanged since DefaultWindowManager recreates JFrames. A bonus is already available : all frames keeps their status with WidgetState, and it's more easy to close the plugin when the frame is closed.
This change is mainly programmer-oriented, but you can already see the new 'Windows' menu in Main Interface.
A MDI window manager has also been implemented. It is ugly, unfinished, and of course not activated by default. There is no config option, we have to set it explicitely in the source to use it, but hey, it works, that proves that the WindowManager interface does its jobs, and that's all we needed ;)
