post replacement: add "Replace Image" dialog to post sidebar.

app/views/moderator/post/posts/_replace.html.erb

@@ -0,0 +1,11 @@
+<%= simple_form_for(@post, url: replace_moderator_post_post_path, method: :post) do |f| %>
+  <h1>Replace Image</h1>
+
+  <p>
+    Delete the current image and replace it with another one, keeping
+    everything else in the post intact. This is meant for upgrading
+    lower-quality images, such as image samples, to higher-quality versions.
+  </p>
+
+  <%= f.input :source, label: "New Source", input_html: { value: "" } %>
+<% end %>

app/views/moderator/post/posts/replace.html.erb

@@ -0,0 +1,5 @@
+<div id="c-moderator-post-posts">
+  <div id="a-replace">
+    <%= render "moderator/post/posts/replace" %>
+  </div>
+</div>

app/views/posts/partials/show/_options.html.erb

@@ -55,6 +55,8 @@
         <li><%= link_to "Expunge", expunge_moderator_post_post_path(:post_id => post.id), :remote => true, :method => :post, :id => "expunge", :data => {:confirm => "This will permanently delete this post (meaning the file will be deleted). Are you sure you want to delete this post?"} %></li>
       <% end %>
 
+      <li><%= link_to "Replace Image", replace_moderator_post_post_path(:post_id => post.id), :id => "replace-image" %></li>
+
       <li id="mobile-version-list"><%= link_to "Mobile version", mobile_post_path(post) %></li>
     <% end %>
   <% end %>

app/views/posts/show.html.erb

@@ -121,6 +121,10 @@
     <%= render "post_appeals/new", post_appeal: @post.appeals.new %>
   </div>
 
+  <div id="replace-image-dialog" class="prose" title="Replace image" style="display: none;">
+    <%= render "moderator/post/posts/replace" %>
+  </div>
+
   <div id="add-to-pool-dialog" title="Add to pool" style="display: none;">
     <%= render "pool_elements/new" %>
   </div>