[sugar] Issues with the presence service

[Marco Pesenti Gritti]

Hi,

yesterday I got back most of the network related functionality in sugar. 
It's still easy to break and needs cleanup. Anyway, here are some issues 
I had:

- We need a way to get basic informations about the activity, before 
joining it,  the title at very least. Might just use the service 
properties for this? Maybe a get_title api in Activity?

Btw I'm somewhat confused by this in Activity:

def get_icon(self):
    return self._buddy.getIcon()

- We need a way to get the activity default type, so we can figure out 
which activity to associate to the service.

- I had to make some hacky changes to share_activity. For udp services 
we need to publish the group IP in the properties (unless there is a 
better way?). Have a look at how I'm doing it currently... I'm sure we 
can clean it up.

- There seem to be no way to join an activity other than manually 
duplicate the service. Also should we provide this rather than have 
every activity to reimplement it? In sugar.activity.Activity or maybe 
even directly in the shell...

If there are already good ways to do these please correct me.

Marco