upgrade minimum nodejs version, yarn dev deps

Looks like I basically had to do this to keep up. With nodejs version 12
(current LTS), the version of fsevents I installed wouldn't build. A
"yarn upgrade" by itself resulted in a new problem as described in #69.
Conversely, the new versions don't install with nodejs 8. So I bit the
bullet and upgraded all the dev dependency stuff and the nodejs at once.
nodejs 10 seems capable of running either the old or new, fwiw.

I'm a little sad that this seems to have made the UI bundle 5% larger.
Before, "yarn build" said 350 KiB. After, 369 KiB. A little bit in
several places. For example, jquery-ui.bundle.js went from 156 KiB (in
2 chunks) to 160 KiB (in 1 chunk) for some reason.

webpack/base.config.js

@@ -49,10 +49,17 @@ module.exports = {
         test: /\.js$/,
         loader: 'babel-loader',
         query: {
-          presets: ['env', {modules: false}],
+          presets: [
+            ['@babel/preset-env', {
+              targets: {
+                esmodules: true,
+              },
+              modules: false
+            }]
+          ],
         },
         exclude: /(node_modules|bower_components)/,
-        include: ['./ui-src'],
+        include: [path.resolve('./ui-src')],
       },
       {
         test: /\.png$/,

webpack/prod.config.js

@@ -35,7 +35,7 @@ const CompressionPlugin = require('compression-webpack-plugin');
 const baseConfig = require('./base.config.js');
 const merge = require('webpack-merge');
 
-const CleanWebpackPlugin = require('clean-webpack-plugin');
+const { CleanWebpackPlugin } = require('clean-webpack-plugin');
 
 module.exports = (env, args) => {
   return merge(baseConfig, {
@@ -88,7 +88,7 @@ module.exports = (env, args) => {
     plugins: [
       new CleanWebpackPlugin(),
       new CompressionPlugin({
-        asset: '[path].gz[query]',
+        filename: '[path].gz[query]',
         algorithm: 'gzip',
         test: /\.js$|\.css$|\.html$/,
         threshold: 10240,