nailgun network_groups model requires enum

[Andrew Woodward]

nailgun network_groups model requires name as enum, this prevents adding additional networks as prescribed in the multi-l3 network treatment

NetworkGroup.name should be changed from Enum to String(50)

[Andrew Woodward (xarses)]

moving this from enum might not be the correct direction. Aflter Ryan and I went through the code more, the name field is used more like a type. The more effective change may be to rename the column to type and add another column to track the 'display name' of the network