Change the alert panels

- move the alert panels (duplicate, out of scope) to be above the tabs
- if both panels are present, combine them in one
- change the styling to match the 'important note' pattern in mainstream publisher

This uses the "important note" pattern that was first introduced in Publisher.

Before:

![image](https://cloud.githubusercontent.com/assets/23801/5129101/827a67ea-70d7-11e4-92fc-023ab9a57f2e.png)

![image](https://cloud.githubusercontent.com/assets/23801/5129156/05ded58a-70d8-11e4-920a-8623580caafc.png)

After:

![image](https://cloud.githubusercontent.com/assets/23801/5129079/661d595e-70d7-11e4-8890-b7a56bf1969d.png)

![image](https://cloud.githubusercontent.com/assets/23801/5129073/52365c4c-70d7-11e4-887f-3f03f2d61419.png)

/cc @fofr

I'm not sure it should still be called `important-note`, if we were abstracting it out into the govuk_admin_template I'd name it something more abstract that relates to how it looks. eg `pull-out-note` or `callout`. The styles are based on those in the Bootstrap docs: http://getbootstrap.com/components/#glyphicons-how-to-use