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/javascript/src/styles/base/040_colors.css

@@ -88,8 +88,6 @@
 
   --diff-list-added-color: green;
   --diff-list-removed-color: red;
-  --diff-list-obsolete-added-color: darkGreen;
-  --diff-list-obsolete-removed-color: darkRed;
 
   --wiki-page-versions-diff-del-background: #FCC;
   --wiki-page-versions-diff-ins-background: #CFC;
@@ -301,8 +299,6 @@ body[data-current-user-theme="dark"] {
 
   --diff-list-added-color: var(--green-1);
   --diff-list-removed-color: var(--red-1);
-  --diff-list-obsolete-added-color: var(--green-3);
-  --diff-list-obsolete-removed-color: var(--red-3);
 
   --dtext-blockquote-background: var(--grey-3);
   --dtext-blockquote-border: 1px solid var(--grey-4);

app/javascript/src/styles/common/diffs.scss

@@ -5,20 +5,12 @@
     margin-right: 0.5em;
   }
 
-  .added.obsolete, .added.obsolete a {
-    color: var(--diff-list-obsolete-added-color);
-  }
-
   .removed, .removed a {
     color: var(--diff-list-removed-color);
     text-decoration: line-through;
     margin-right: 0.5em;
   }
 
-  .removed.obsolete, .removed.obsolete a {
-    color: var(--diff-list-obsolete-removed-color);
-  }
-
   ins, ins a {
     color: var(--diff-list-added-color);
     text-decoration: none;
@@ -30,14 +22,6 @@
     text-decoration: line-through;
     margin-right: 0.5em;
   }
-
-  ins.obsolete, ins.obsolete a {
-    color: var(--diff-list-obsolete-added-color);
-  }
-
-  del.obsolete, del.obsolete a {
-    color: var(--diff-list-obsolete-removed-color);
-  }
 }
 
 .diff-body {

app/javascript/src/styles/common/versions.scss

@@ -3,7 +3,7 @@ body.a-index {
     display: flex;
 
     table.striped {
-      flex: 1; 
+      flex: 1;
     }
   }
 
@@ -11,3 +11,15 @@ body.a-index {
     margin-top: 2em;
   }
 }
+
+div#version-comparisons {
+  margin-bottom: 1em;
+
+  span {
+    font-weight: bold;
+  }
+
+  ul#version-comparisons-list, ul#version-comparisons-list li {
+    display: inline;
+  }
+}

app/javascript/src/styles/specific/wiki_page_versions.scss

@@ -9,10 +9,6 @@ div#c-wiki-page-versions {
       background: var(--wiki-page-versions-diff-ins-background);
       text-decoration: none;
     }
-
-    ul.wiki-other-names-diff-list li.obsolete {
-      text-decoration: dotted underline;
-    }
   }
 
   #a-index {