Mobius-client

Core:

* Fixed Challenge transaction memo passing during transaction build https://github.com/mobius-network/mobius-client-js/pull/3/commits/2151e467c39cc893b02c764cbb1b6b95c35a6358

* Added tests for authentification parts https://github.com/mobius-network/mobius-client-js/pull/3

Core:

* Improved build setup, added ESlint, Prettier https://github.com/mobius-network/mobius-client-js/pull/1

* Implemented core authentification functionality which allows generate & validate Challenge transactions on the developer's and sign it on user's side https://github.com/mobius-network/mobius-client-js/pull/2