Change default behaviour of TemplateController.view to 404.

[icmurray]

The current behaviour of TemplateController?.view() (which is the fallback controller should all others fail) is to attempt to render (as a genshi template) the requested file.

Although this may be a feature that some instances want. In general, it leads to:

• 500s when attempting to access a normal template (eg - ​http://datahub.io/importer/preview)
• A way of inadvertantly serving things you may not want to serve. (Small risk, as it needs to be renderable as a genshi template).

Solution:

• Change the controller to 404
• Ensure there's a way for existing ckan instances to override that behaviour should they need it.