Remove webpack

[yufengwng]

Webpack was originally used to compile and bundle up the javascript, so we can serve it up to a webpage. However, now we are going to be running within a webview inside vscode. The html we load inside the webview can access files in our extension folder, so we don't really need to use webpack to bundle things. Once we convert files to typescript in #8, we should be able to reference the output files from typescript.