DEV: port full-width component to be included directly (#126)

Removes the [full-width
component](https://github.com/discourse/discourse-full-width-component)
dependency by adding most of the code directly to the theme. There was
one grid definition in the CSS I ended up removing because it was
conflicting with an existing override in the theme.

Anyone who has previously installed the theme should manually remove the
full-width component from it.

about.json

@@ -13,8 +13,7 @@
     "serialize_topic_is_hot": true
   },
   "components": [
-    "https://github.com/discourse/discourse-sidebar-new-topic-button.git",
-    "https://github.com/discourse/discourse-full-width-component.git"
+    "https://github.com/discourse/discourse-sidebar-new-topic-button.git"
   ],
   "color_schemes": {
     "Horizon": {
@@ -138,4 +137,4 @@
       "hover": "584B3E"
     }
   }
-}
+}