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
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html