[Orchestra] SpringSingleConversationScope

[Simon Kitching]

Hi Mario,

A while ago you added class SpringSingleConversationScope to orchestra 
with the comment "Mostly useful for dialog/flow frameworks".

Do we still want this class? I'm not sure what it would be used for; 
AFAIK the intention is to use a "nested conversation context" for 
flows/dialogs, and in that case we can use the normal 
SpringConversationScope class.

Unless there is something I've missed, we can remove this class (it has 
never been in a released Orchestra version).

Thanks,
Simon