Add config parameter to make it possible to turn off auto accounting
Add help texts to some of the more advanced rendering settings
Wrap all conference pages in a rendering function

This removes a lot of redundant references to ConferenceContext, and
makes it easier to make further changes that affect all conf pages.
Add functionality to completely override confreg templates

This makes it possible for a conference to completely re-render for example
what a form looks like.

The easiest to do is still to inherit from the base template, and that's what
should mostly be used. But it's now possible to override an individual template
if necessary (for example the registration form), while keeping the base template
for the majority of the pages.