Drama types

The drama list should be implemented as a list of <: AbstractDrama objects, not a list of functions.

Then we have two methods that should be implemented for all AbstractDrama subtypes:

struct MyDramaType <: AbstractDrama
  ...
end

check_drama(source::MyDramaType, context::DramaContext) = # not sure what it should return

should_check_drama(source::MyDramaType, context::DramaContext) = true / false # depending on whether the check_drama function should run. This can be used to skip tests