Make the post versions more like the old format

- "Current" is now most like the old format
-- It is therefore now the default for post versions
- Only show the actual edits in their own column
- Show the current state at that version in another column
- On the "previous" view, don't double-show full list of tags for
  the first post versions, so leave edits blank

app/models/post_version.rb

@@ -130,6 +130,19 @@ class PostVersion < ApplicationRecord
     }
   end
 
+  def pretty_rating
+    case rating
+    when "q"
+      "Questionable"
+
+    when "e"
+      "Explicit"
+
+    when "s"
+      "Safe"
+    end
+  end
+
   def changes
     delta = {
       :added_tags => added_tags,