Additions for electrical metering

[danjhugo]

I would like to propose a couple of minor additions for electrical metering purposes...

1. Add a class brick:Electrical_Energy_Sensor, as a subclass of brick:Energy_Sensor.

2. Add "peak" to the list of literals in brick:AggregationShape (i.e. allow "peak" to be the object of a triple with predicate brick:aggregationFunction). 

3. Rename brick:PowerComplexityShape to be brick:ElectricalComplexityShape, and rename brick:PowerFlowShape to be brick:ElectricalFlowShape. 

Rationale for these changes...

1. An Electrical_Energy_Sensor is a mathematical integration of Electrical_Power_Sensor, and is a type that is more specific than brick:Energy_Sensor. It's a type that we have required in our project work, and which we have used internally in our own patches to Brick. 

2. Peak aggregation was a project requirement we encountered, and it seems like a common need others will have. This allows a modeller to set an aggregation over any metering Point, rather than being limited to brick:Peak_* classes.

3. This is just a minor detail about clarity. These shapes are not really specific to 'power' as distinct from energy, but concern electricity in general (whether energy or power). I know renaming classes is discouraged, but these shapes are 'internal' in the sense that they're used by automated validation tools rather than being referenced in models, so I think this refactoring should be safe.

Please let me know what you think!

[gtfierro]

1. Sounds good! Easy enough to add
2. We have the max aggregation entity property pattern, as exemplified here. Does this solve your issue?
3. I think this is fair; I can introduce the change in a PR and we can discuss with the broader community

[gtfierro]

@danhugo there is already an Electric_Power_Sensor in Brick; be sure to check out the nightly build

[gtfierro]

@danjhugo can you leave some feedback on #425 to see if this fits your needs? Thanks!