Performance enhancements

• device: when updating, only add/remove new endpoints/configrules, not all (reduce num inserts)

• service: when updating, only add/remove new endpoints/constraints/configrules, not all (reduce num inserts)

• slice: when updating, only add/remove new endpoints/constraints/configrules, not all (reduce num inserts)

• add methods retrieving a summary of devices, services, slices (i.e. without endpoints, constraints, config rules, subslices, subservices, etc.)