known hosts list does not cope well with large numbers of hosts

I have hundreds of entries in my ssh known hosts file and when I expand the known hosts item in the connect dialog's treeview, the window is several times the size of my screen, in both directions. I suggest the following:

 * not show the key
 * place the treeview inside a gtk.ScrolledWindow
 * pack widgets into the parent VBox using pack_start() rather than add, so the ScrolledWindow (and thus the TreeView) can be told to expand to fill all available window space when the window is made bigger.

Also, for kicks, it would be nice if the list of hosts was sorted.

Attached is a patch which does all of the above.