Scaling gallery processor should not depend on Wicket

Currently, the scaling gallery processor (that create multiple resized variants of uploaded images) uses the org.hippoecm.editor.type.JcrTypeStore to determine which imageset variants to create. The JcrTypeStore retrieves a JCR session from the Wicket session. The scaling gallery processor is therefore effectively tied to Wicket, and cannot be used outside a Wicket application (e.g. in an importer).

Instead, the JcrTypeStore should not rely on Wicket to retrieve the JCR session to use.