[feature request] Add Support for Litecoin's MWEB (Mimble Wimble Extension Blocks) for added privacy

[mvozzo]

I'm a huge fan of Stack Wallet because it prides itself on being a Privacy focussed wallet that supports some of the best privacy coins.

Please add to the roadmap support for Litecoin's MWEB (MimbleWimble extension blocks). This will allow Stack Wallet user to be able to send and received LTC privately between each other. I think this will drive a lot of adoption of Stack wallet in the Litecoin community.

Here's short 2 min video on how it works within the Lite Wallet (for those unaware of this optional privacy feature). https://www.youtube.com/watch?v=n3giboWvnro

[hectorchu]

See #860