Base defaultavatar text on displayname

Fix #4876

core/avatar/controller.php

 			$image->show();
 		} else {
 			// Signalizes $.avatar() to display a defaultavatar
-			\OC_JSON::success();
+			\OC_JSON::success(array("data"=> array("displayname"=> \OC_User::getDisplayName($user)) ));
 		}
 	}
 

core/js/jquery.avatar.js

 			var url = OC.Router.generate('core_avatar_get', {user: user, size: size})+'?requesttoken='+oc_requesttoken;
 			$.get(url, function(result) {
 				if (typeof(result) === 'object') {
-					$div.placeholder(user);
+					if (result.data && result.data.displayname) {
+						$div.placeholder(user, result.data.displayname);
+					} else {
+						$div.placeholder(user);
+					}
 				} else {
 					if (ie8fix === true) {
 						$div.html('<img src="'+url+'#'+Math.floor(Math.random()*1000)+'">');

settings/js/personal.js

                 $('#oldDisplayName').text($('#displayName').val());
                 // update displayName on the top right expand button
                 $('#expandDisplayName').text($('#displayName').val());
+		updateAvatar();
             }
             else{
                 $('#newdisplayname').val(data.data.displayName);