Automatically Calculate Charge for Supercharging

Please add automatic calculations for the charges for supercharging since it the fees are posted and Teslafi already records the amount of kWh or how long (and charge rate) the session was.  If a specific charge session didn't cost money, we can override it.  

To know which cars have free supercharging, it could be an account setting (default to yes for S/X/P3 and no for 3/3D)