Instrument connection fixes

1. Function connectDevice(this, interface, address) is introduced in the MyInstrument class. Correspondingly, connectTCPIP and connectUSB are deleted from MyScope class
2. In order to use the ObjectConstructorName, returned by the instrhwfind(), for device connection specify now 'constructor' as interface
3. Device object is initialized to struct() for consistency
4. In configureDefaultVisa checks for the existence of properties is added