Add alternate comparison types to versions

- The types are:
-- Previous: The default and the previously used type
-- Subsequent: Compares against the next version
-- Current: Compares against the current version
- Allow switching between comparison types in index and diff views
-- Have links vary depending upon current comparison type

app/views/note_versions/_listing.html.erb

@@ -14,16 +14,16 @@
         <% end %>
       <% end %>
       <% t.column "Body", td: {class: "col-expand diff-body"} do |note_version| %>
-        <%= diff_body_html(note_version, note_version.previous, :body) %>
+        <%= note_version_body_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Position (X,Y)", width: "5%", column: "position" do |note_version| %>
-        <%= note_version_position_diff(note_version) %>
+        <%= note_version_position_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Size (WxH)", width: "5%", column: "size"  do |note_version| %>
-        <%= note_version_size_diff(note_version) %>
+        <%= note_version_size_diff(note_version, params[:type]) %>
       <% end %>
       <% t.column "Changes", width: "3%" do |note_version| %>
-        <%= status_diff_html(note_version) %>
+        <%= status_diff_html(note_version, params[:type]) %>
       <% end %>
       <% t.column "Updated", width: "10%" do |note_version| %>
         <div>

app/views/note_versions/index.html.erb

@@ -2,6 +2,8 @@
   <div id="a-index">
     <h1>Note History</h1>
 
+    <%= render "versions/types" %>
+
     <%= render "listing" %>
 
     <%= numbered_paginator(@note_versions) %>