Break out device apps

[mchack-work]

Break out the device apps to their own repos:

• [x] blink
• [x] nx
• [x] random
• [x] rng_stream
• [x] signer
• [x] timer

Take special care of signer and include the hash in -apps and the checks there so we don't change the resulting binary unnecessarily.

[mchack-work]

signer now here: https://github.com/tillitis/tkey-device-signer

Not yet removed from apps.