Bergamot as npm module

[jelmervdl]

This reorganises this project as pure javascript: just import bergamot-translator as an NPM module.

Depends on https://github.com/browsermt/bergamot-translator/pull/437

Additional benefits:

• Easier for people at home to build the extension! No more need to compile wasm
• Easier to use other npm modules (to a degree… we're still running in an not very familiar environment)

Downsides:

• webpack. It's like cmake in terms of being able to figure out why stuff doesn't work.