GUI-200

implemented changes from UI review, detailed in issue

- default to first AZ
- don't require description on snapshot
- suggested device name should be default. Only works when instance known, no client side updates for attach to arbitrary instance from volume page
- should list instance and volume on dialog (fixed on instance and volume detail pages)
- It would be great to list volume ID as well as the name (which is listed) (also fixed on vol detail page)