Update notices to success or danger flash messages

Be clearer about a success or failure using Bootstrap alert styles.

`:notice` and `:alert` are still used by inherited_resources and responders gems, customising the flash keys doesn’t work because of the old versions being used.

* Explicitly set :success or :danger flash messages in app
* Coerce :notice to a success message
* Coerce :alert to a danger one

![screen shot 2014-11-19 at 10 38 53](https://cloud.githubusercontent.com/assets/319055/5104275/4f8128ba-6fd8-11e4-9fcb-dae3996cfe02.png)