500 error in dashboard_activity_list_html (Fixes #256)

This does not return 500 anymore, which is great. But I've just run into interesting problems.

* ~~The tests render `templates_legacy/activity_streams/activity_stream_items.html` instead of `templates/activity_streams/activity_stream_items.html`~~
* When I set an offset of 1, it prints `<li class=\"load-less\"><a href=\"/packages?id=2048f54a-a259-457e-aa54-535ba77a57ba&amp;offset=-28\" class=\"btn btn-rounded\">Load less</a></li>` which is from https://github.com/okfn/ckan/blob/master/ckan/templates/activity_streams/activity_stream_items.html#L5. Whatever this is meant to link to, I'm pretty certain it's wrong.

Fixes #256 

Does anyone have insights on this?