#18 Allow users to set AMI permissions

[Jason Fulghum]

User's can't set AMI permissions from the AMI Browser view.

This involves:
- a new menu item to set permissions when an AMI is clicked on (only enabled for the owner of the AMI)
- a new dialog to allow the user to set permissions in a similar style to the AWS management console's AMI permissions dialog ( http://console.aws.amazon.com )
- EC2 service call to update the permissions based on changes