Improvements to notifications. Finishes [#75446202].

Improvements to notifications:
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Story:
https://www.pivotaltracker.com/story/show/75446202

Demo:
https://s3-eu-west-1.amazonaws.com/uploads-eu.hipchat.com/22685/874180/z6zerZbLOPCWjnP/notification_with_close.mov

- Removed automatic fadeout for notifications
- Added close button
- Display message after register on notification instead of inside modal dialog
- Fixed markup for confirm account modal dialo