[#1838] Always create full-text search indexes

Before this, we only created FTS indexes when the user sent a `indexes` or
`primary_key` parameter to the `datastore_create` call, which only happens when
you're directly calling it (i.e. not uploading a file through CKAN's
interface).

This makes it faster to upload something to the datastore, but creates problems
as queries aren't on indexed fields. So this commit changes it to always create
at least the full-text search indexes.