Clean up webpack deployment

Fixes #15 (closed): webpack externals excluded too much and forced usage of npm install in deployment environment.

Now, does not use any externals; all packages are bundled as expected. One unusual tweak to webpack config was necessary for 'node-fetch' to get properly bundled: a mainFields: ['main', 'module'] override, as detailed here: https://github.com/node-fetch/node-fetch/issues/450#issuecomment-494475397