FritzboxAHA-Binding improvement: Added energy reading for webinterface queries.

I wass missing the energy reading from fritzbox (FritzOS < 6.0). This patch brings it. 

To be able to switch between different time ranges, I added some optional parameter to the fritzaha item config. I don't know if this works for other boxes (I own a 7270 v3 with OS 5.54), but I believe, with FritzOS < 6 it is the only way to retrieve energy readings.