Webpack (#1367)

* Replace gulp with webpack and npm scripts for JS compilation
* Set up Travis CI to commit compiled JS
* Restructure `js` directory; only one instance of npm, forum/admin are "submodules"
* Refactor JS initializers into Application subclasses
* Maintain partial compatibility API (importing from absolute paths) for extensions
* Remove minification responsibility from PHP asset compiler
* Restructure `less` directory

less/common/Alert.less

@@ -0,0 +1,63 @@
+.Alert {
+  padding: 12px 16px;
+  border-radius: @border-radius;
+  line-height: 1.5;
+
+  .Alert--color(@alert-color, @alert-bg);
+}
+.Alert--error {
+  .Alert--color(@alert-error-color, @alert-error-bg);
+}
+.Alert--success {
+  .Alert--color(@alert-success-color, @alert-success-bg);
+
+  a, a:hover {
+    text-decoration: underline;
+  }
+}
+.Alert--color(@color; @background) {
+  background: @background;
+
+  &,
+  a,
+  a:hover,
+  .Button,
+  .Button:hover,
+  .Button:active,
+  .Button.active,
+  .Button:focus,
+  .Button.focus {
+    color: @color;
+  }
+}
+.Alert-controls {
+  list-style-type: none;
+  padding: 0;
+  margin: 0 -8px 0 8px;
+  display: inline-block;
+
+  > li {
+    display: inline-block;
+    margin: 0 5px;
+
+    > a, > .Button {
+      text-transform: uppercase;
+      font-size: 12px;
+      font-weight: bold;
+
+      &.disabled {
+        cursor: default;
+        text-decoration: none;
+        opacity: 0.5;
+      }
+      &:hover {
+        text-decoration: underline;
+      }
+    }
+
+    > .Button {
+      margin: -10px;
+      vertical-align: 0;
+    }
+  }
+}