Create an easy way to init/edit configuration variables

[pedroferreira1]

We should make it easy for the user to init the lib from a server, from the mainnet/testnet default (offline), from a custom set of configurations.

Then we would have some constants, e.g. HATHOR_BIP44_CODE and others that can be edited, e.g. MAX_OUTPUTS, GAP_LIMIT, ...

Discussion in PR: #110 (comment)

[luislhl]

I think we fixed this in #265

Do you think there is any additional change needed for this issue, @pedroferreira1 ?