General update with a few changes

Yo.

It will work out of the box now, and has template preset settings for the Beez templates, otherwise works as normal.

Some things to note:

It is now a system plugin using the onBeforeRender event, which means it fires in admin as well, but it makes a check if it isn't the site application.

Re-jigged the url business a bit, so we now create the next link and add it to the document, but actually it doesn't even use it. The path function creates it from some new InfiniteConfig variables so it's only there to stop the script from dying.

There are a couple of fields for the loading and finish texts, and a field to select which categories it should be active for (default is all, with none selected) to give a modicum of control as it's a bit broad now, and could be troublesome to implement on an existing site.

Make sure that it doesn't break for you before accepting the pull request, as there are only the two of us available to test ;)