Enhancement: Get financial results of period

[ArdJonker]

V2G Liberty users would like to see the financial result of using the app. Typically the last 7 days (as Joris showed with his research).
As FlexMeasures already logs all needed information (charge power, availability and hourly prices) and calculates earnings, the FM client can retrieve this information.

The request should somehow contain the period (start/ end or duration).
The result should contain total charged kWh and cost, dis-charged kWh and cost and average availability in this period.
Preferably these cost include client specific cost structure (markup / kWh and VAT) or could these be calculated locally?

This assumable is not specific to V2G Liberty.