Enhancement: generic BIP-32 support

[coolaj86]

Currently we support BIP-44 style HD Paths:

m/44'/<coin>'/<account>'/<use>/<index>

m/44'/5'/0'/0/0

BIP-32 allows arbitrary levels of depth, and is not restricted to a particular purpose.

Currently not implemented because the command line use is optimized for supporting Dash. However, if there's a strong use case, we could support generic BIP-32 style paths - probably best through a different utility.