Upgrade vue-loader for bug fixes and a simpler webpack config

The new vue-loader no longer requires a redundant config for babel-loader, style-loader, etc in order to function. This means we no longer have to split out our babel config into a separate .babelrc file and rely on environment variables to conditionally include plugins and presets (a solution which is deprecated in babel 7).

To Do:

• Upgrade vue-loader to v15
• Adjust webpack.config.js, replace references to style-loader with vue-style-loader (a light fork of style-loader, see documentation here)
• [ ] Migrate .babelrc config back to webpack.config.js and adjust karma's config to apply its own babel configuration.