Take sensor label as additional GET parameter when asking for most recent value

Very small feature request to improve the existing module a bit:

Currently, you can make a GET request to a sensor (instead of a POST) and it will return the most recent data from that sensor. However, it will return the most recent data point for EACH label. So if you are sending both "temperature" and "humidity", it will send both in a JSON packet structure.

In some cases, you may not want to receive all the latest values, you may just one a specific one. So by providing an additional GET parameter input, you could specify which one you want to filter down to, and only return that one.