Implements IP Address Group CLI.

Extends CLI for creating / deleting an IP Address group, and adding /
deleting IP addresses to the group. For more info, please refer to
https://midobugs.atlassian.net/browse/MN-1078

Fix MN-1078

Change-Id: I38ab6b9c9b85ad53175f289ed48576860246e929
Merge pull request #96 from midokura/dev/tomohiko/ip_addr_group_cli_master/20140123

Implements IP Address Group CLI.