iron-ajax accessibility issues

[lpalmaro]

Audit results: [Severe] Elements with ARIA roles must use a valid, non-abstract ARIA role (1) [Warning] Text elements should have a reasonable contrast ratio (1) [Warning] The purpose of each link should be clear from the link text (1) Not applicable tests (10) Passing tests (4)

The alt text for the link is "link image watch". It should be something a bit more descriptive about where the user will be taken upon clicking. This is less a concern about the demo page and more that the developer should just be sure to use better labels there.

[notwaldorf]

I'll transition this to use iron-demo-helper/demo-snippets and clean up the demo a bit while we're at it.