Recent Tracker enhancements

We've added a few new features to Tracker recently, including:

- New balloon pop up for rejecting stories
- New dashboard landing page, with release notes and other news. You can bypass this page by changing the "Start Page" preference on the "my settings" page
- The velocity override widget is more streamlined, and takes up a bit less space. To override or revert velocity, click on the Velocity link.
- Member list pagination on the project settings page (50 members per page).