Add whitelist/exclusion flagging

[Kris Deugau]

For long-term use, add a "white" flag.

For netblocks, this prevents export of that block, or excludes it from a larger listing with automatic or manual flags.

For IPs, this exports it as an exclude from any container flags.

Needs investigation on how to flag an entry as excluded in rbldnsd.

[Kris Deugau]

Mostly implemented in r66 and r71, with possible minor polish in other commits around the same time.