Add post image upload interface (#12)

Adds accessible drag-and-drop and browse controls, staged attachment editing, responsive lazy-loaded thread image grids, and UI regression coverage.

Reviewed-on: #12
Co-authored-by: codegirl-007 <s.raide@gmail.com>

templates/question.html

@@ -17,6 +17,7 @@
         {{if isEdited .Question}}<span class="edited">Edited</span>{{end}}
       </p>
       <p class="post-body">{{.Question.Body}}</p>
+      {{template "postImages" .Question}}
       {{template "postActions" (postCtx .User .CSRF .Question .Question 0)}}
     </div>
   </article>