[web] implement cross origin resource sharing (CORS) (closes #2491768)
Partial implementation that is enough to get started but leaves out
some of the advanced features like caching and non-simple methods
and headers.
.. _cwprops:
The property mecanism
---------------------
.. XXX CWProperty and co
Property API
~~~~~~~~~~~~
.. XXX feed me
Registering and using your own property
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. XXX feed me