Pass view_name to extra_body_script hook (#443)

At the moment it's not easy to tell whether the hook is being called
in (for example) the row or table view, as in both cases the
`database` and `table` parameters are provided.

This passes the `view_name` added in #441 to the `extra_body_script`
hook.

datasette/views/base.py

@@ -94,6 +94,7 @@ class RenderMixin(HTTPMethodView):
             template=template.name,
             database=context.get("database"),
             table=context.get("table"),
+            view_name=self.name,
             datasette=self.ds
         ):
             body_scripts.append(jinja2.Markup(script))