[SàT dev] [en] important updates

[Goffi]

G'day,

I have done a huge refactoring in the backend, mainly about discovery but also 
with entities cache (see commits).

The discovery change are explained enough in the commits, but some precisions 
about entities cache; before there was a mess between bare jid and resources, 
so I have changed that:
	- entity cache now always use the full jid, if you need to access 
bare_jid information, you have to use userhostJID yourself
	- when a resource is accessed, the bare jid cache is updated with 2 keys: 
"LAST_RESOURCE" which contain the last used resource, and "resources" which 
containt a set of all the resources which were active during the session.

I have also done a lot of cleaning. These changes should bring some bugs, the 
time to fixe the usage everywhere, but they should quickly fix a lot of them...

Cheers
Goffi