…s on MISP standard format

- Adding a note or an opinion will always add the
  new analyst data object to the list of notes or
  opinions at the parent data layer level
- `from_dict` on a JSON blob is also able to parse
  properly analyst data and generate flat lists
  regardless of whether the given data described
  in the new flat or previously nested format

- Additional checks for parent to support both
  the standalone and attached analyst data objects
- Standalone Analyst data objects with nested
  notes or opinions are defined with the nesting
  as they have no parent. When they are added to
  a parent data layer, the nested objects are then
  flattened

…ts lists back to the mixin parent class