use metameta class for registry

[mikofski]

define _meta_names as class attribute, then use metaclass __new__ method to add them to attributes.

Meta names can also be used by data_readers to propagate data attributes, especially if all data sources parameters (and parameter files) have same structure.

[mikofski]

• This seems like a good idea since for every single registry, the attributes are the same as the meta_names, and that's the only thing that happens in the constructor.
• However using meta class unless necessary seems overkill here, unless making new registry is something that developers will do often, say when making custom layers (plugins/middleware)
• meta names is required by layers, so
  • declare registry meta in init, then collect them into meta names in superclass somehow
  • declare registry meta as class attr, then collect them into meta names in meta class (*)
  • declare meta names and then use meta class to make attributes

(*) this seems best, because user is actually stating attributes rather than having them magically created