Add multi-site support to ckan

[nils.toedtmann]

Currently, each ckan site needs its own ckan wsgi process. That eats a lot of resources where many ckan sites are served from one machine (e.g. eu3).

That would dramatically change if a ckan process could behave like multiple ckans (e.g. like Apache's "<VirtualHost?>", or tracd). Depending on the "Host:" header in the HTTP1.1 request, it would choose which local ckan ini file to obey.

I see two ways to constitute the map hostname-to-ini-file map:

• ckan reads a set of ini files, and each ini file declares which servers names it is responsible for
• In a global ini file, there are directives mapping servernames to ini files.

In either case there should be a global ckan ini having the default settings for all local ckan sites. Each site ini could be very short then, just having e.g. title, name, database credentials, active plugins etc.

[nils.toedtmann]

this is similar, but not equal to #1096

[nils.toedtmann]

See also ​http://ckan.okfnpad.org/multisite