Tweak dataset listings

Only show activities if relevant, fix file size display
Fix problems with redirects on members page

When redirecting from /organizationto to /publisher we are losing the
query string. I didn't find a way to kkep it, so I changed the URLs on
the templates.
Fix publishers page pagination

Hack alert: the group controller does not currently offer a way to
customize the pagination links (we need a proper IGroupForm interface
with types support), so on the meantime we tweak the output of the
default pagination from a helper function.
Add Last Modified to order by list in publisher page

Since fa3ca5be in CKAN core the default oredering is score/ metadata
modified, and this does not appear in the order dropdown.