Add `Reporter` classes to handle common reports

[victorgarcia98]

Recently, the introduction of the Reporter and PandasReporter classes in PR #641 opens the door to define report generation logic, in a standardized fashion. Even though both classes come with a great flexibility, they require a long list of arguments that might be similar (if not the same) across different use-cases.

For that reason, It would be nice to create a series of simple report generation classes that cover most of the practical applications and that require as little input arguments as possible. Some ideas for simple handy reporters:

• SimplePandasReporter: drops levels other than event_value
• AggregateReporter: Aggregate (min, max, mean, sum, ...) the data of all the sensors that are input.
• EnergyBillReporter: Computes the price of energy of a given sensor using the energy tariff, tolls, taxes, levies, etc...

With all this, I'd like to invite you to discuss which reporter classes we should prioritize and what functionality they should include.

[nhoening]

I think this is exactly the right course of action.

• Maybe this can be converted into a discussion? (there is a button on the right for that). It might lead to several issues.
• Instead of SimplePandasReporter we could say ValueReporter? Why bring up pandas in this abstraction?
• How about a CO2Reporter which reports overall CO2 and CO2/kWh?