Initial documentation of presence service overview.

Fix weird indent in server_plugin module

services/presence/__init__.py

@@ -0,0 +1,36 @@
+"""Service to track buddies and activities on the network
+
+Model objects:
+
+    activity.Activity -- tracks a (shared/shareable) activity
+        with many properties and observable events
+    
+    buddy.Buddy -- tracks a reference to a particular actor
+        on the network
+        
+        buddy.GenericOwner -- actor who owns a particular 
+            activity on the network 
+        
+        buddy.ShellOwner -- actor who owns the local machine
+            connects to the owner module (on the server)
+    
+Controller objects:
+
+    presenceservice.PresenceService -- controller which connects 
+        a networking plugin to a DBUS service.  Generates events 
+        for networking events, forwards updates/requests to the 
+        server plugin.
+    
+    server_plugin.ServerPlugin -- implementation of networking 
+        plugin using telepathy Python (Jabber) to provide the 
+        underlying communications layer.  Generates GObject 
+        events that the PresenceService observes to forward onto 
+        the DBUS clients.
+
+Utility machinery:
+
+    buddyiconcache.BuddyIconCache -- caches buddy icons on disk
+        based on the "jid" XXX Jabber ID? of the buddy.
+    
+    psutils -- trivial function to decode int-list to characters
+"""