Preventing noise in logs from cocoon.handled and DSpaceI18NTransformer

Prevent at least one cause of 

     ERROR cocoon.handled @ Failed to process pipeline
        at <map:serialize type="xml"> - resource://aspects/Feedback/sitemap.xmap:135:40

Also prevents

    WARN  org.dspace.app.xmlui.cocoon.DSpaceI18NTransformer @ Translation not found for attribute title in element <img>