hooks: allow to set the duration of the gritter notification when a new chat message arrives

This is done adding a new "duration" parameter to the chatNewMessage() client
side hook.

doc/api/hooks_client-side.md

@@ -223,6 +223,7 @@ Things in context:
 4. sticky (boolean) - if you want the gritter notification bubble to fade out on its own or just sit there
 5. timestamp - the timestamp of the chat message
 6. timeStr - the timestamp as a formatted string
+7. duration - for how long in milliseconds should the gritter notification appear (0 to disable)
 
 This hook is called on the client side whenever a chat message is received from the server. It can be used to create different notifications for chat messages.
 

src/static/js/chat.js

@@ -149,7 +149,8 @@ var chat = (function()
         "text" : text,
         "sticky" : false,
         "timestamp" : msg.time,
-        "timeStr" : timeStr
+        "timeStr" : timeStr,
+        "duration" : 4000
       }
 
       // is the users focus already in the chatbox?
@@ -186,7 +187,7 @@ var chat = (function()
           count++;
           $("#chatcounter").text(count);
 
-          if(!chatOpen) {
+          if(!chatOpen && ctx.duration > 0) {
             $.gritter.add({
               // (string | mandatory) the heading of the notification
               title: ctx.authorName,
@@ -195,7 +196,7 @@ var chat = (function()
               // (bool | optional) if you want it to fade out on its own or just sit there
               sticky: ctx.sticky,
               // (int | optional) the time you want it to be alive for before fading out
-              time: '4000'
+              time: ctx.duration
             });
           }
         }