Removed high contrast handling in Toaster fixes #158

    - removed .dj_a11y in Toaster css
    - changed the documentation
    - remove icon container in template
Removed isAriaListbox flag, fixes #210

- Removed isAriaListbox flag
- updated doc and samples
various fixes

- found out that most part of tests/unit/list/AriaListbox.js was failing but due to a `return` missing
- also found out that my changes were breaking that test (I broke selection in my last commit, but didn't notice)
- fixed the part of the code that overrides the role attributes when set in the DOM, added something in the tests to check that a when a role attribute is set in the DOM it's doesn't get overridden in the rendering phase.