Added announcement template

Design: https://projects.invisionapp.com/d/main#/console/1392015/34940936/preview

Homepage: 
![screen shot 2014-10-17 at 12 59 55 pm](https://cloud.githubusercontent.com/assets/910510/4682681/9cd744dc-561f-11e4-807d-8502534a1f15.png)


Course page: 
![screen shot 2014-10-17 at 1 03 39 pm](https://cloud.githubusercontent.com/assets/910510/4682682/a202e970-561f-11e4-8781-18fef19320ef.png)


@marcotuts please advice on the design for the course pages as well as the dismiss icon/link.

@dsjen @rocha @shnayder 
Is it bad if we add the CSRF token regardless of the the method? We may not need the extra logic if there are no side effects from adding the token.