Render titles with source links for TIMDEX records

Why these changes are being introduced:

In TIMDEX UI, titles linked to full record views. That feature is not
currently implemented in USE UI.

Relevant ticket(s):

* [USE-99](https://mitlibraries.atlassian.net/browse/USE-99)

How this addresses that need:

This updates TIMDEX title links to use the `source_link` field.

Side effects of this change:

When developing TIMDEX UI, we decided not to test any view logic. I've
continued that practice here, with some apprehension. (We've already
missed a bug in the view while developing USE, which might have been
avoided with more robust integration testing.) Not exactly a side
effect, but perhaps a topic for future discussion.

Author: jazairi

app/views/search/_result.html.erb

@@ -1,7 +1,12 @@
 <li class="result">
   <div class="result-content">
     <h3 class="record-title">
-      <span class="sr">Title: </span><%= link_to(result['title'], record_path(result['identifier'])) %>
+      <span class="sr">Title: </span>
+      <% if result['source_link'] %>
+        <%= link_to(result['title'], result['source_link']) %>
+      <% else %>
+        <%= result['title'] %>
+      <% end %>
     </h3>
 
     <p class="pub-info">