Added Melange front page edit view where you can change title, content, feed url. Created SiteSettings and Document models and some logic for them. Added isFeedURLValid function in soc/logic/feed.py. Created some functions for handling datastore updates of different kinds of Models (soc/logic/model.py). Fixed some typos and too long lines of code. Patch by: Pawel Solyga Review by: to-be-reviewed

"""Error types for dispatcher mechanism
"""

class DispatcherError(Exception):
    """Base class for all Dispatcher errors"""
class DispatcherKeyError(KeyError, DispatcherError):
    """Error raised when unknown (sender,signal) set specified"""
class DispatcherTypeError(TypeError, DispatcherError):
    """Error raised when inappropriate signal-type specified (None)"""