More maven plugins (and site skins)

I've created a couple of site skins, one that looks like this blog for my use, and one that's much simpler and blue for use with Sea Glass documentation.

I've also created a successor to my HTML Filter Site plugin called docbkx-wrapper-plugin that wraps the Docbkx plugin so that you only need the one plugin.

Also, I've created a Git Site Wagon plugin that allows you to easily deploy maven site documentation to the pages system of GitHub, so that it can be kept with the project as a top-level branch.

There are things that could be better done in the docbkx wrapper, but since site documentation will be changing quite a bit in Maven 3, I'm not inclined to put more effort into it until that is released.