Accessibility improvements to status message

There are 2 accessibility issues that needs to be looked at. I included a patch that attempts to fix both.

Section wrapper

Wetkit_bootstrap is using <div> instead of <section>.

When looking at the official WET-BOEW Alerts documentation: http://wet-boew.github.io/wet-boew-styleguide/v4/design/alerts-en.html

The Alerts are wrapped in <section> element. This is essential because the alerts include a H4 that can be displayed before the H1 on the page.

Close button

While not part of WET-BOEW, the ability to dismiss a message box via the X is useful but has been reported to case accessibility issues.

There is a “X” that closes the “Attention” message. The “X” is identified as “a link” with NVDA and “link TIMES” with JAWS 16, the alt text should be more descriptive for the screen reader user. CEA recommends for example: “Close attention message” would be more appropriate.
Source code: ×

Status message

WCAG 2.0 Reference:
1.1.1 Non-Text Content
3.3.2 Labels or Instructions

I'm unsure if this is the best way to do it but the patch adds an aria-hidden="true" to the close link for screen readers to simply ignore it.

Other possibility

We could also provide a title attribute that dynamically reflect the header of this box (To avoid repeating the same title on multiple alert boxes on the same page).

Thoughts?