Update to modern ESnet logo / branding.

Fixes #728.

docs/_esnet/templates/layout.html

@@ -102,7 +102,7 @@
   <div class="container">
     <div class="row">
       <div class="col-md-1">
-        <a href="http://www.es.net/"><img src="_static/logo-esnet.png" alt="[ESnet]"></a>
+        <a href="http://www.es.net/"><img src="_static/ESnet_Final_Logos_All_Blue_Circle_Stamp_RGB.png" alt="[ESnet]"></a>
       </div>
       <div class="col-md-11">
         <p class="pull-right">

docs/conf.py

@@ -128,7 +128,7 @@ html_theme_path = sphinx_bootstrap_theme.get_html_theme_path()
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-html_logo = "_esnet/static/logo-esnet-ball-sm.png"
+html_logo = "_esnet/static/ESnet_Final_Logos_All_Blue_Circle_Stamp_RGB.png"
 
 
 # The name of an image file (within the static path) to use as favicon of the