Add optional serial numbers to client.lights.scan()

[hhartikainen]

API documentation states:

"1.3. Search for new lights
1.3.2. Body as of 1.1 (Optional)
{"deviceid":["45AF34","543636","34AFBE"]}
Note: The maxiumum number of serial numbers in any request is 10."

Using serial numbers allows adding lights that have already been added to another bridge or cannot be found for some other reason.

[sqmk]

Should be feasible for me to add. Expect this shortly.