Extended ‘<img>’ elements for the Pharo logo in the ‘index-teaser’ an…

…d ‘navbar’ templates to have a file for scale 2.

site/templates/index-teaser

@@ -1,6 +1,6 @@
 <div class="teaser">
     <div class="main">
-        <img class="img-responsive" src="/web/files/pharo.png" alt="logo"/>
+        <img class="img-responsive" src="/web/files/pharo.png" alt="logo" srcset="/web/files/pharo-2x.png 2x"/>
         <h1>The immersive programming experience</h1>
         <p style="font-size: smaller"> 
 Pharo is a pure object-oriented programming language <i>and</i> a powerful environment, focused on simplicity and immediate feedback (think IDE and OS rolled into one).<br/>

site/templates/navbar

@@ -7,7 +7,7 @@
         <span class="icon-bar"></span>
         <span class="icon-bar"></span>
       </button>
-      <a class="navbar-brand" href="/web"><img src="/web/files/pharo-logo-small.png" alt="Pharo"/></a>
+      <a class="navbar-brand" href="/web"><img src="/web/files/pharo-logo-small.png" alt="Pharo" srcset="/web/files/pharo-logo-small-2x.png 2x"/></a>
     </div>    
 
     <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">