CORS support

[rgrp]

This is what you do in Apache. Should do this in lib/base.py or similar.

    Header always set Access-Control-Allow-Origin "*"
    Header always set Access-Control-Allow-Methods "POST, PUT, GET, OPTIONS"
    Header always set Access-Control-Allow-Headers "X-CKAN-API-KEY"

    # Respond to all OPTIONS requests with 200 OK
    # This could be done in the webapp
    # This is need for pre-flighted requests (POSTs/PUTs)
    RewriteEngine On
    RewriteCond %{REQUEST_METHOD} OPTIONS
    RewriteRule ^(.*)$ $1 [R=200,L]