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/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;
+  }
+}