RFC for initial components of reservations

This set of patches defines:

- utilities for reserve/release completely based on existing acl
- wiring them to GUI on the host detail and host list pages 
- some other minor implementation utilities

Next step is to wire reservation to create job page (ui and CLI) so user can declare that he wants to reserve the system when the job is actually started on a host.

Finally the general plan is to add ability for the reservation to be time based.

Any comments are welcome.