Make it possible to put the site in maintenance mode
By specifying the UTC date from which the maintenance shoulds start,
developers can put the site in 'maintenance' mode.
Also redirect to /maintenance if we get a CapabilityDisabledError.
Patch by: Sverre Rabbelier
Make use of decorators.view for all views
This gives us a 'view' hook where we can do things that need to be
done for all views (such as catching certain exceptions, or checking
for maintenance mode).
Patch by: Sverre Rabbelier