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/helpers/pool_versions_helper.rb

@@ -0,0 +1,31 @@
+module PoolVersionsHelper
+  def pool_version_show_diff(pool_version)
+    previous = pool_version.previous
+    previous.present? && pool_version.description != previous.description
+  end
+
+  def pool_version_name_diff(pool_version)
+    previous = pool_version.previous
+    if previous.present? && (pool_version.name != previous.name)
+      name_diff = diff_name_html(pool_version.pretty_name, previous.pretty_name)
+      %(<br><br><b>Rename:</b><br>&ensp;#{name_diff}</p>).html_safe
+    else
+      ""
+    end
+  end
+
+  def pool_version_post_diff(pool_version)
+    previous = pool_version.previous
+    diff = {}
+
+    if previous.present?
+      diff[:added_post_ids] = pool_version.post_ids - previous.post_ids
+      diff[:removed_post_ids] = previous.post_ids - pool_version.post_ids
+    else
+      diff[:added_post_ids] = pool_version.added_post_ids
+      diff[:removed_post_ids] = pool_version.removed_post_ids
+    end
+
+    render "pool_versions/diff", diff: diff
+  end
+end