Generators: decorators should respect `--model-name`

[Alexander-Senko]

Description

Decorator will respect --model-name passed to scaffold_controller or controller generator.

That could be of a particular use to solve namespace issues (e.g. when controllers are namespaced and models are not).

The specs have been refactored to reduce and DRY the code.

Testing

1. Use controller or scaffold_controller generator with --model-name option.
2. Check if the generated decorator matches the model name.

To-Dos

• [x] tests

References

• #919