Properly output errors when the main thread receives some

Use the ui.error infrastructure that has been put in place and use
ui.terminate even if we received an Exception, so that we can output the
list of errors that we have. This does away with 2 now unused functions
in ui/UIBase.py

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/init.py

@@ -347,7 +347,8 @@ class OfflineImap:
         except (SystemExit):
             raise
         except Exception, e:
-            ui.mainException()
+            ui.error(e)
+            ui.terminate()
 
     def sync_singlethreaded(self, accs, config):
         """Executed if we do not want a separate syncmaster thread