Allow rule override to be scoped.
Fix a bug where rules are not properly returned for single IP.
Since the `ip_address >> operator` only works for IP classes.
In order to compare both classes and single IP, ``>>=`` operator
should be used instead.
Add rules system for evaluating rules based on IP address.
The rules system currently support two type of rules:
* Ban — disallow matched IP address to post in a board.
* Override — override board status for a certain IP address.
Each rule may be trigger on/off and may specify active period.