Bugfix for updating sensor names

[tengelmeier]

Sorry, had to discover that updating sensor names was problematic.

This PR includes:

• An fix for updating already cached sensor names
• The possibility to add an optional 'uuid prefix' in config.json so HomeKit doesn't get confused with if you add a second home bridge instance mapped to the same Aqara gateway

[snOOrz]

This issue can be fixed by deleting ~/.homebridge/accessories/cachedAccessories so I don't think this change is necessary.

[djrams10]

For me, even deleting the file homebridge / accessories / cachedAccessories the problem always comes back. I really know more how to do it. Someone to help me please? thank you