Classification graphs: support different workspaces
Classification editor: fix links for static icon files

These links have changed with the "djangofication" of the static files.
Ontology/Classification editor: don't save initial project id
Ontology/Classification editor: only change workspace if container is available
Ontology editor: only load tree from init() if pid was passed
Ontology tools: update widget workspaces properly when loading
Ontology editor: propery clear trees array in init() method
Ontology widget: initialize without PID; let tool handle this
Classification editor: add setup check before display

If the classification system is not setup correctly for the current
project, the editor offers now to create all the needed classed and
relations.