Add segwit xpub magic for litecoin and digibyte

[kaladinlight]

There is currently no sewgit_p2sh or segwit_native xpub magic enabled for litecoin and digibyte resulting in the inability to get public keys in the correct format using the corresponding coin name.

Update https://github.com/keepkey/keepkey-firmware/blob/master/include/keepkey/firmware/coins.def to support the following:

• Litecoin enable: xpub_magic_segwit_p2sh = 28471030, xpub_magic_segwit_native = 78792518
• Digibyte enable: xpub_magic_segwit_p2sh = 77429938, xpub_magic_segwit_native = 78792518

I am not familiar enough with the firmware to know if there would be any additional fallout by enabling or if it would just follow the same code paths as bitcoin which does have them enabled already...

[markrypt0]

I verified the magic numbers and will include this in the next release which should happen today or tomorrow.