Add temporary conference banner

_layouts/base-en.html

@@ -88,6 +88,7 @@ menu:
         <a href="/en/support-bitcoin"><img src="/img/but_involve.svg" alt="Support Bitcoin">Support Bitcoin</a>
       </div>
     </div>
+    <a href="http://bitcoin2013.com" class="conferencebanner"><img src="/img/bitcoin2013_banner.png" alt="Bitcoin conference"></a>
     <div id="footer"><div>© Bitcoin Project 2009–2013 Released under the <a href="http://creativecommons.org/licenses/MIT/" target="_blank">MIT license</a></div></div>
   </div>
   <script type="text/javascript">svgfallback();</script>

_less/screen.less

@@ -571,6 +571,11 @@ li{
 	-webkit-border-radius:9px;
 }
 
+.conferencebanner{
+	float:right;
+	margin-right:5px;
+}
+
 /*Styles specific to mobiles*/
 
 @media handheld, only screen and (max-device-height: 37em), only screen and (max-device-width: 50em){
@@ -660,4 +665,9 @@ li{
 	.preview{
 		display:none;
 	}
+	.conferencebanner{
+		float:none;
+		display:inline-block;
+		margin:0px 0px 10px 0px;
+	}
 }