Move more logic to the helper modules

- Diff view changes
-- Only show pool description changes in diff view
-- Conditionally render diff link when applicable values are changed
-- Conditionally show diff view sections when values are changed
- Show renames on index view
-- There is plenty of space
-- This wasn't shown at all for wikis
-- Having to navigate to an alternate page is unwieldy for pools
- Show "posts" as a status on pools
-- This is so all changes among versions are quantified as a status
- Standardize diff/index titles

app/models/pool_version.rb

@@ -89,23 +89,6 @@ class PoolVersion < ApplicationRecord
     normalize_name(name).mb_chars.downcase
   end
 
-  def build_diff(other = previous)
-    diff = {}
-
-    if other.nil?
-      diff[:added_post_ids] = added_post_ids
-      diff[:removed_post_ids] = removed_post_ids
-      diff[:added_desc] = description
-    else
-      diff[:added_post_ids] = post_ids - other.post_ids
-      diff[:removed_post_ids] = other.post_ids - post_ids
-      diff[:added_desc] = description
-      diff[:removed_desc] = other.description
-    end
-
-    diff
-  end
-
   def previous
     @previous ||= begin
       PoolVersion.where("pool_id = ? and version < ?", pool_id, version).order("version desc").limit(1).to_a
@@ -115,6 +98,7 @@ class PoolVersion < ApplicationRecord
 
   def self.status_fields
     {
+      posts_changed: "Posts",
       name: "Renamed",
       description: "Description",
       was_deleted: "Deleted",
@@ -124,6 +108,10 @@ class PoolVersion < ApplicationRecord
     }
   end
 
+  def posts_changed
+    ((post_ids - previous.post_ids) | (previous.post_ids - post_ids)).length > 0
+  end
+
   def was_deleted
     is_deleted && !previous.is_deleted
   end
@@ -140,10 +128,6 @@ class PoolVersion < ApplicationRecord
     !is_active && previous.is_active
   end
 
-  def text_field_changed
-    previous.present? && (name_changed || description_changed)
-  end
-
   def pretty_name
     name.tr("_", " ")
   end