Export resume dates in <content>, and in a custom element so Mahara <-> Mahara transfers will be able to work 100%.

(cherry picked from commit a42825eb8b44a0299ded915136a6c928fff21437)

Throw UserExceptions if the exporter is asked to export artefacts or views not belonging to the user.

Now only the people who should be able to delete wall posts can. The
site admins can delete any post, users can delete any post on their
wall, and any of their posts on someone else's wall.

removed all the unused images from raw/
removed all the duplicate images from default/, as well as the unused
ones.

also cleaned up the css to point to the new image locations.

and moved some images into artefact/interaction plugins where they
belong.

that is, things that are also present in raw.  this makes it a lot
smaller and takes better use of css's cascading.  almost certainly
deleted some stuff i shouldn't have :)

Tweaked forum pages to include this stylesheet.

Tweak relevant pages so they include those rules - including
user/view.php which should really be provided by artefact/internal.

Previously, when a user uploaded a file, it would be added to their used
quota, even if it was a group or institution file.

This makes sure the right stylesheet is included.

This makes things much more consistent, and means we can use the
SECTION_PLUGINTYPE and SECTION_PLUGINNAME constants to hook in the right
stylesheets.

There are a few outstanding issues, these will be resolved as part of
the massive theme overhaul before Mahara 1.2 is released

There are a few outstanding issues, these will be resolved as part of
the massive theme overhaul before Mahara 1.2 is released

There are a few outstanding issues, these will be resolved as part of
the massive theme overhaul before Mahara 1.2 is released

There are a few outstanding issues, these will be resolved as part of
the massive theme overhaul before Mahara 1.2 is released

This idea comes from the themes contributed by Paul Walker. In the
interests of minimising the delta in the templates, it makes sense to
just apply it to the default theme.