Stop using deprecated set_request_property
Add an easy way to check in request if management

There are certain places where there is a need to check and see if we
are visiting the management interface, having an handy object on the
request helps solve that problem.
Remove old pregenerator
Add Site as a model, which can have Domains

We want to have the concept of a Site, which is where information is
stored about the Site such as the title/tagline and any other future
information.

Domain's now belong to a site. This allows many domains to point at a
single site.
An Entry now is tied to a Site, not a domain
Change MainRoot to filter based on Site
Create subscribers sub-directory

This is where all the subscribers for various events will be living.
When matched_route is None, it has no .name
Add route and subscriber predicates
Move calls to add_{routes,views,events} after fixing up config

These functions should be the last things that get added to the config.
Add new predicates, and start using them. Remove old ones.
config.scan for subscribers.