Major CSS revamp

- Get rid of Bootstrap (except we still rely on some JS)
- Use BEM class names
- Rework variables/theme config
- Fix various bugs, including some on mobile

The CSS is still not ideal – it needs to be cleaned up some more. But
that can be a focus for after beta.

less/forum/IndexPage.less

@@ -0,0 +1,37 @@
+// ------------------------------------
+// Sidebar
+
+@media @desktop-up {
+  .IndexPage-nav .item-newDiscussion .Button {
+    display: block;
+    width: 100%;
+    margin-bottom: 20px;
+  }
+}
+
+// ------------------------------------
+// Results
+
+.IndexPage-toolbar {
+  margin-bottom: 15px;
+}
+.IndexPage-toolbar-view, .IndexPage-toolbar-action {
+  display: inline-block;
+  margin: 0;
+  list-style: none;
+  padding: 0;
+
+  > li {
+    display: inline-block;
+  }
+}
+.IndexPage-toolbar-view > li {
+  margin-right: 5px;
+}
+.IndexPage-toolbar-action {
+  float: right;
+
+  > li {
+    margin-left: 5px;
+  }
+}