Highlight state considation

This builds on #1729 and makes our language a lot more consistent. For my sanity.
Here, we are switching one Annotator Highlight method for another, thereby changing the defined semantics of the annotator highlight API. (But we mask this change by doing other changes in our CSS.)

If we want to change the semantics of these methods in (our fork of) Annotator, I think we should do that there first.

But I would rather not do it at all (at this time), because (as I have said repeatedly), the Annotator branch we are currently shipping with is heavily obsolete legacy code, *even inside the scope of our fork*, so adding any further changes to that branch will create extra work for us, when we will have to merge our branches, or collect changes from them in the future.

So I say we should just let it alone for now, until we can finally consolidate those branches.

Looking at it from that angle, maybe we can get away with this stealthy semantic change (masked by the CSS change), but I can't say I like it.