support markov targets with identical names on different servers

markov targets are queried and autogenerated based on chatter, but had a
legacy name which is no longer in use for this, preferring the foreign
keys to channel and consequently server. the name is really just
informative these days, but was still being used to find targets, and
thus was breaking when two servers had the same channel name in them.
this fixes that

ircbot/models.py

@@ -118,7 +118,7 @@ class IrcChannel(models.Model):
 
     def __str__(self):
         """Provide string representation."""
-        return "{0:s}".format(self.name)
+        return "{0:s} on {1:s}".format(self.name, self.server.name)
 
 
 class IrcPlugin(models.Model):