Hardening the method for getting pattern index files

Add a check to determine if the page is branch. If it is, then it's
an index page for a pattern and should be included.

Author: danmacpherson

layouts/partials/patterns-browser.html

@@ -22,7 +22,8 @@ <h1 class="pf-c-title pf-m-4xl">
         </div>
       </div>
     <div class="pf-c-content" >
-      {{ $patterns := where $.Pages "Section" "patterns"}}
+      {{ $patterns := where $.Pages "Type" "patterns"}}
+      {{ $patterns := where $patterns "BundleType" "branch"}}
       <div class="pf-l-stack pf-m-gutter">
         <div class="pf-l-stack__item pf-u-text-align-right pattern-count-style">
           <span id="pattern-count">{{- len $patterns -}}</span> of {{ len $patterns }}  patterns displayed