Allow prefixing of entity name/ids

[alexandre-leites]

This edit allow HA prefixing of our entities so you can group them together easily or have more than one google fit sensor grouped correctly.

With this edit I have the following sensors:

• sensor.alexandre_calories
• sensor.alexandre_distance
• sensor.alexandre_height
• sensor.alexandre_steps
• sensor.alexandre_time
• sensor.alexandre_weight

[hemantkamalakar]

Thanks a lot @xalexslx