Uniform node and browser module imports with rollup

[armaniferrante]

Currently, we have some utility modules that dispatch based based upon whether we're in a browser environment or not. We should be able to remove these by configuring Rollup to import the modules correctly.

For example, we we import tweetnacl like this with this file.

Also our EventEmitter imports need fixing (e.g., see #25), as they are causing us to use any types.

[armaniferrante]

Mostly done by #73.

The last thing we should do here is replace this file with an import: https://github.com/oasislabs/oasis-client/blob/master/packages/confidential/src/tweetnacl.ts

[armaniferrante]

Another one de69353#diff-81ec44e2202d86803f3d36efd4d65ddbR3.