Bundle change for Firefox

[SebastienGllmt]

Note: This PR is based on feature/webpackFour so we can't merge it until the new WASM bindings are done & merged

Background

Historically we haven't been able to submit to Mozilla's addon page because they require every individual file to be < 4MBs. To achieve this in a reasonable way, it made the most sense to upgrade to webpack 4 first but we couldn't do that until we also upgraded the WASM bindings (non-trivial!). However, now that it's all done, we should finally be able to submit!

Contents of this PR

1. I use the webpack4 splitChunks feature to ensure all files are < 4MBs.
2. I remove our use of pug for dynamically create HTML at compile time. Instead, I use HtmlWebpackPlugin because it natively has the ability to generate HTLM script includes for every chunk of your application.
3. I added caching to the babel compilation of our development branch. This made npm run dev run about 20 seconds faster.
4. Upgrade our bip39 library since the latest version allows us to remove non-English languages. This makes our code a bit smaller but more importantly some non-English languages were triggering Firefox's illegal word policy so this increases our chance of the app being accepted.

Things to consider

I wasn't able to apply the chunking to the dll folder. It looks like the concept of splitting up your code into chunks is NOT supported by the webpack DllPlugin. I tried googling it and most people suggest to just stop using the DllPlugin and rely only on the new chunking system. There are a few complications to this and what I have now in this PR is good enough for Firefox but we will have to figure something out for this because there's nothing stopping it from growing to over 4MBs for one file.

Firefox result

Firefox gives us the okay to submit. All the warnings are unavoidable.