Detect continuous aggregates and build the nested classes for them

[jonatas]

Today, if the continuous_aggregates macro is not declared in the model, it cannot detect previous aggregations or even use them on the fly.

It would be great if we could detect them and build their nested classes.

To disable it:

class MyHypertable < Hypertable
  acts_as_hypertable ..., detect_aggregates: false 
end

By default, when acts_as_hypertable is invoked, it allows fetching the continuous aggregates directly from the hypertable nested classes.

MyHypertable::MyCaggWithDifferentPattern.all