Add Seam level Exception Interceptor

When Exception correctly bubble to the UI layer, the default Exception Filter is too high in the stack : all we can do is display an error page.
This is usefull as a "last line of defense", but this is not enough if we want to handle the Exception at application level.

We could do explicit Exception handing in all Seam Beans, but for a transversal requirement like Quota Check this would not be easy.

So, we should leverage Seam interceptors to do Automatic Exception handling.

This will also probably require us to introduce a new type of ClientException that contains the needed info for the Intercepror to know what it has to do.