[NEO3] Definition of COIN field for BIP32 child key derivation paths

[lllwvlvwlll]

Summary or problem description
For neo2, we have defined 888' for the COIN field for the BIP32 compliant derivation proposals. Since we are diverging from using common keys with #1419 , I would also like to propose that we change the coin field to make the distinction even more clear.

Do you have any solution you want to propose?
887' is available per https://github.com/satoshilabs/slips/blob/master/slip-0044.md

Neo Version

• Neo 3

Where in the software does this update applies to?
key derivation