[Android] Data modes with andflmsg

[Cosmicaero]

Purpose: to enable the use of kv4p-ht for digital communications, leveraging the data modes, message formatting and image capabilities of andflmsg.

[VanceVagell]

Thanks for the idea! These modes seem more niche than others, so although I think it'd be really fun to play with they make more sense in a variant of the project (i.e. a fork). Adding "variant" tag so people who want this can fork the project to add it.

That said, I do want to add more digital stuff to the mainline app, such as image support. But it's likely to use more standard transports like AX.25 packet.