Remove fieldset handling code, support generic alternative and Vertical Tabs

This was originally added because it was something I needed at the time and sort of fitted within this module.

I'd be open for suggestions and thoughts, I know there is a better solution.

The collapsing options are pretty much outside of this module's declared scope; I was going to suggest we pull that out too.

What would we need to do to support Vertical Tabs? Now we're using the same form names, do we need to do anything in fact? won't installing Vertical Tabs just take over?

Not entirely. I just ran across this after installing vertical tabs on a site with this module.

The use case is that a node author has ability to change the date of their node, but not its author.

Normally, vertical tabs takes what's usually in the "authoring" section (author + post date) and displays the author's name in the tab title.

With the ability to change the author disabled, upon creating a new node, the "authoring" vertical tab displays "By Anonymous" as the author (see attached screenshot), even though if one saves the node, it is indeed created by the correct author.

There may be other similar vertical tabs displays that this affects, but this is the one I noticed.

OK. Posted here: #1132826: Vertical Tabs displays generic/incorrect summary when field is not present