feat: web client refresh (#1476)

Give the web client a major overhaul.

User-visible highlights include:

* Mobile is now fully supported.
* Added fullscreen support on mobile.
* Better support for dark mode.
* Added mime icons to the torrent list.
* Improved theme consistency across the app.

Maintainer highlights include:

* Updated code to use ES6 APIs.
* No longer uses jQuery UI.
* No longer uses jQuery.
* Use Webpack to bundle the Javascript, CSS, and assets together -- the entire bundle size is now 68K gzipped.
* Added eslint / prettier / stylelint tooling.
* Uses torrent-get's 'table' mode for more efficient RPC calls.

web/stylelint.config.js

@@ -0,0 +1,49 @@
+
+module.exports = {
+  "extends": [
+    "stylelint-config-sass-guidelines",
+    "stylelint-config-prettier"
+  ],
+  "plugins":  [
+    "stylelint-config-primer/plugins/no-undefined-vars",
+    "stylelint-config-primer/plugins/no-unused-vars"
+  ],
+  "rules": {
+    "block-no-empty": true,
+    "color-no-invalid-hex": true,
+    "comment-no-empty": true,
+    "declaration-block-no-duplicate-properties": true,
+    "declaration-block-no-shorthand-property-overrides": true,
+    "font-family-no-duplicate-names": true,
+    "function-calc-no-invalid": true,
+    "function-calc-no-unspaced-operator": true,
+    "function-linear-gradient-no-nonstandard-direction": true,
+    "max-nesting-depth": null,
+    "media-feature-name-no-unknown": true,
+    "no-duplicate-at-import-rules": true,
+    "no-duplicate-selectors": null,
+    "no-empty-source": true,
+    "no-extra-semicolons": true,
+    "no-invalid-double-slash-comments": true,
+    "primer/no-undefined-vars": true,
+    "primer/no-unused-vars": true,
+    "property-no-unknown": true,
+    "scss/at-rule-no-unknown": true,
+    "selector-attribute-quotes": null,
+    "selector-max-compound-selectors": null,
+    "selector-max-id": null,
+    "selector-no-qualifying-type": [
+      true,
+      {
+        "ignore": [
+          "attribute"
+        ]
+      }
+    ],
+    "selector-pseudo-class-no-unknown": true,
+    "selector-pseudo-element-no-unknown": true,
+    "selector-type-no-unknown": true,
+    "string-no-newline": true,
+    "unit-no-unknown": true,
+  }
+};