Accessibility issues with FilteredSelectMultiple widget

[Sarah Boyce]

1. "Available {name}" and "Chosen {name}" are h2 elements when this doesn't make sense for the html structure (makes them too important) (See headers video file)
2. The select boxes have no labels, they should be labelled by "Available {name}" and "Chosen {name}" (see "Other issues" video file)
3. "Choose all" is not related to it's tooltip help text (see "Other issues" video file)
4. The help text "Hold down “Control”, or “Command” on a Mac, to select more than one." should be associated to the select box(es) (see "Other issues" video file)

Possibly the whole thing should be a fieldset with a legend