Minor changes to align with W3C Last Call Working Draft 12 September 2013

Web Notifications
- adds lang attribute
- replace titleDir, titleDir by generic dir attribute

Jira-issue: API-40
Adds readonly attributes to notifications object.

Jira-issue: API-40
Adds nullable flag to attributes of the NotificationOptions dictionary.

Jira-issue: API-40
Merge pull request #39 from mlasak/API-40

Minor changes to align with W3C Last Call Working Draft 12 September 201...