simple subnets
Simple Subnets UI
Simple Subnets validations
Simple Subnets: fix network_address validation
Simple Subnets: UI fixes

- Makes the "New Subnet" button green
- Adds inline help for "Network Address"
- Sets "External DHCP" as the default value for dhpc_server
Merge pull request #338 from ares/simple_subnets_backend

Simple subnets backend