Refactor Transaction from @dashevo/dashcore-lib for modern browsers

[coolaj86]

We want our own Transaction mechanism, but built for modern node and modern browsers.

• [ ] Reduce code to minimal dependency graph
• [ ] Native where possible
  • [ ] BN
  • [ ] crypto / webcrypto
  • [ ] nix lodash
• [ ] Dependency injection (Interfaces) where not
  • [ ] secp256k
  • [ ] ripe160md
• [ ] Nix this / classes

[coolaj86]

It's a miracle! https://github.com/DashHive/DashTx.js #25