Default platform value when creating devices

[decoupca]

examples:

1. when creating a device from a device_type manufactured by juniper, junos is the default platform value
2. when creating a device from device_type = C9300L-24P-4X, default platform = ios.

Achieving no.2 looks straightforward, add a default_platform property of device_type objects, & then I edit the C9300L-24P-4X object to the ios default platform.

To achieve no.1 most elegantly, maybe we could have an inheritance model. Set default platform for a manufacturer, optionally overridden by device_type.

So manufacturer cisco could have default_platform = ios, which shows up when creating a new device_type with manufacturer = cisco. We can then leave at ios, or select nxos, as appropriate. then any devices created from that device_type get that default_platform when created.

Thoughts?