Add command line option --dry-run

And set the [general]dry-run=True setting if yes. It is not used yet.
Also set ui.dryrun to True so we can output what WE WOULD HAVE DONE in
dryrun mode.

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

offlineimap/ui/UIBase.py

@@ -48,6 +48,8 @@ def getglobalui():
 class UIBase(object):
     def __init__(self, config, loglevel = logging.INFO):
         self.config = config
+        # Is this a 'dryrun'?
+        self.dryrun = config.getboolean('general', 'dry-run')
         self.debuglist = []
         """list of debugtypes we are supposed to log"""
         self.debugmessages = {}