(sramp-160) Change artifact's 'delete' action to be a logical delete

Changed artifact delete to be a logical rather than a hard delete.  The
artifact JCR node is now stripped of its sramp mixin type and moved from
/s-ramp/ to /s-ramp-trash/.  The move isn't strictly necessary but it
was an easy way to make sure getArtifact wouldn't be able to find it.