Add AirspyHF support

[rmivdc]

Since AirspyR2 and AirspyMini are already supported,

Would it be also possible to add AirspyHF support ?

[redawl]

I'm interested in working on this feature if someone hasn't already started. I'm very new to open source development, however: Anything I should be aware of?

I do think I have a general idea of how to implement the feature, but I also might not know how much I don't know :)

[jopohl]

@redawl do you have an AirspyHF available for testing? Happy to walk you through a Pull Request to get this supported in URH.

[redawl]

I do! I will get started on the dev work.