focusability and roles should be attributed by common-panel-set

[bkardell]

As per discussion with @stevefaulkner and @LJWatson we decided that common-panel itself shouldn't necessarily have most of the tabindex/affordances, but rather these should be granted to them by the container panel set. Update the spec, check the prototype.

[LJWatson]

@bkardell
Think this can be closed, based on introduction of the <paneltitle> element?

[bkardell]

I've based the unit/regression tests on the current implementation - can we verify the state of the panels themselves (the ones not in panelsets) in the demo and note specifically which if any changes need to be made in order to determine whether this issue can be closed?