ctl-district: act on many nodes with one invocation

A simple enhancement to help with oo-admin-ctl-district:
https://trello.com/c/HWlGpenH/135-5-add-all-nodes-to-district-quickly

Now you can specify multiple nodes to act on at once; also, add-node
can automatically create the district first.
ctl-district: add --available and list-available

Further functionality for oo-admin-ctl-district:
https://trello.com/c/HWlGpenH/135-5-add-all-nodes-to-district-quickly

Can add-node --available and all nodes of right profile will be added.

list-available cmd shows undistricted nodes (optionally, for one profile)