proposed IP address tracking changes

[ivan at 420.am]

Kristian (and others) - 

What do you think of the following changes?

- Add a table FS::addr or FS::ip containing individual IP addresses
- Add the block itself to FS::addr_block instead of deriving it from the
  gateway
- Add a table to link additional IPs to svc_* records.  Replace 
  svc_acct.slipip and svc_broadband.ip_addr with foreign keys to this
  table.
- Enhancements to address block web UI: delete blocks, split blocks with
  the ability to specify gateway address, split blocks at arbitrary
  boundries, merge blocks

-- 
_ivan