Refactor CSS (#116)

Refactor CSS files and structure. Also refactors some html and React components for a smarter use of CSS classes.

app/javascript/components/common/PostBoardLabel.tsx

@@ -0,0 +1,11 @@
+import * as React from 'react';
+
+interface Props {
+  name: string;
+}
+
+const PostBoardLabel = ({ name }: Props) => (
+  <span className="badge badgeLight">{name?.toUpperCase()}</span>
+);
+
+export default PostBoardLabel;