ability to import form's parameters and rules

[drzraf]

When an import@ is processed, eg like:

form:
  import@:
    type: partials/form-foo
    context: blueprints://

the form key is extracted and only fields are merged.

So there is no way to avoid repeating rules and form parameters instead of importing them.

Side note: the blueprints import/extends codebase is tremendously hard to catch up.