Fix deduplication of resources on import
On importing resource we shouldn't just disable the copies. All the copies should be available in the database as active, until the user explicitly disables them. Though we should de-duplicate them based on their name-filename-md5 signature when listing them in the model. That can be easily done by simple adding "group by" to the query.
Such solution both fixes legacy presets (bug 446009), and makes importing resources less embarrassing (bug 445367).