[enh] search button icon added

searx/static/css/style.css

   -moz-box-shadow: inset 0 1px 2px rgba(0,0,0,0.6), 0 0 0 4px #dddddd;
   box-shadow: inset 0 1px 2px rgba(0,0,0,0.6), 0 0 0 4px #dddddd;
 }
-#search_submit { position: absolute; top: 3px; right: 3px; border: 0; padding: 6px; border-left: 4px solid #dddddd; }
+#search_submit { position: absolute; top: 6px; right: 3px; border: 0; padding: 6px; background: url('/static/img/search-icon.png'); background-size: 30px 30px;  width: 30px; height: 30px; }
 
 #results { margin-left: 10px; }

searx/templates/search.html

 <form method="post" action="/" id="search_form">
 <div id="search_wrapper">
     <input type="text" class="q" name="q" tabindex="1" autocomplete="off" {% if q %}value="{{ q }}"{% endif %}/>
-    <input type="submit" value="search" id="search_submit" />
+    <input type="submit" value="" id="search_submit" />
 </div>
     <p>
     {% for category in categories %}