Setup webpack/rollup for @arkecosystem/crypto

[faustbrian]

I'm in the process of updating the paper-wallet dependencies and thus some code that needs changes.

Currently it is not possible to use it in the browser as no UMD module exists https://github.com/ArkEcosystem/core/blob/master/packages/crypto/package.json#L19. This can be changed to point to dist/index which solves the issue but results in a huge file as webpack doesn't know how to apply tree-shaking to it once included in other projects.

Either webpack or rollup (preferred) should be setup to build the crypto package for server and browser support.

See https://github.com/Hotell/typescript-lib-starter for reference.