Allow direct snapshot deploy for application devices

*Update:* The original issue was mistaken. The snapshot kebab menu for App-Device snapshots does include the Deploy option. I'm not sure what I was looking at when I didn't have that option.

However, the option is disabled if the device is in developer mode; I think it should be available in that mode - yes I may be editing the flows, but equally, I am making a choice to rollback to a previous version in my work.

The task for this issue is to enable the Deploy option for developer-mode devices. I suspect this won't be straight-forward. We inhibit snapshot updates whilst in developer mode in general (a pipeline deploys snapshot to all devices in a group except those in dev mode). The proposal is *not* to change that behaviour. The change is specifically to allow a user to manually deploy a snapshot via the device's snapshot page.

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~For an application-assigned device the *only* way we have to deploy a new snapshot to the device is via a pipeline.~

~A pipeline does not allow a device to appear twice (ie as both src and dest stage). Because of this, I cannot upload a snapshot for a device and then tell the device to run it.~

~Unintuitively, instead I have to upload the snapshot to a surrogate device/instance and then use that in the src stage of a pipeline to get the snapshot deployed to the device.~

~For an application assigned devices, we should have a 'Deploy Snapshot' option in the kebab menu as we do for instances.~