#428 "+ Add New ......" functionality in more dropdown boxes

[Peawet08]

In Rack View (and other areas) clicking the dropdown to add a device allows you to select only preconfigured devices.

Can the open be added to the dropdown to add a new device at this point similar to the option already ion place to "+ add new VLAN" when adding a new subnet.

This similar functionality should flow through other dropdown boxes where feasible.

e.g: I started to use the Racks functionality, but when adding a device to the rack I have to leave the rack section and go to Devices to add a device before returning to the rack section to populate the rack list. Adding a new device whilst populating the rack would make this easier. I appreciate there is additional information that can be linked to the device like IP address and location (although this should be inherited from the rack location) etc.. but adding that can be done later as a separate admin task.

Thanks for a great product!!!