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/SettingsPage.less

@@ -0,0 +1,25 @@
+.SettingsPage {
+  margin-top: 5px;
+
+  > ul {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+
+    > li {
+      margin-bottom: 40px;
+    }
+  }
+  fieldset > ul {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+  }
+}
+.Settings-account {
+  li {
+    display: inline-block;
+    margin-right: 5px;
+  }
+}
+