Add ecash

[NicolasDorier]

Altcoins integration need to be done in a single file I can easily review like the billion others that have been integrated. I can't accept a PR that modify code outside of it.

[mishfit]

@NicolasDorier this would allow all Altcoins to work like plugins instead of requiring PRs to implement them.

[Kukks]

Too much feature creep into a PR that adds an altcoin. You should reconsider and split into two if you ever want this to get considered to be merged.