Need human readable string emitter label

[daltoncass]

The seid in the signal->emitter is an int. This doesn't work allow for unique emitter labels like MAC addresses or alphanumeric serial numbers. Suggest adding "emitter_label" to signal->emitter to allow for annotating bursts with a usable label for an emitter.

I have this change in a clone, but I don't have permissions to push

[777arc]

First make a fork of this repo (top right of page https://github.com/sigmf/SigMF), then make your change, then you can open a PR on this repo.

[daltoncass]

Done:
#347