gluon-config-mode: replace inline style with class

Replace the inline stylesheet for the public key box on the reboot page
with a CSS class so it can be styled using the theme.

package/gluon-config-mode/generate/usr/lib/lua/luci/view/gluon-config-mode/reboot.htm

@@ -27,7 +27,7 @@ $Id$
           <p>
             @config_mode.msg_pubkey@
           </p>
-          <div style="text-align: left;font-size: 2em;line-height: 1em; background: #f5f5f5; border: 1px solid #ececec; margin-bottom: 0.5em; padding: 0.5em">
+          <div class="the-key">
             # <%=luci.sys.hostname()%>
             <br/>
             <%=pubkey%>