Review dependencies to trim unused code

[jordaaash]

#2 has been fixed by using Webpack's ignore plugin, but the distribution code still includes the entire bip39 dependency's API (e.g. generateMnemonic). This code is unused, but is not being caught by tree-shaking since the npm source of bip39 is JS rather than TypeScript.

The dependency graph of the build output should be analyzed and optimized to remove unused code. This could be accomplished by targeting a Github commit sha for some dependencies like bip39 to use the TS source instead of the npm published version, or extracting only the methods used, inlining them, and relying on the extended dependencies instead (in this particular case, pbkdf2).