cleanup import satements

- conform to PEP8
- explicitly define symbols instead of 'import *'
- remove unused import

Reviewed-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/ui/UIBase.py

@@ -22,7 +22,6 @@ import sys
 import traceback
 import threading
 from StringIO import StringIO
-from Queue import Empty
 import offlineimap
 
 debugtypes = {'':'Other offlineimap related sync messages',