Introduce decorators argument in module()

[gogonzo]

Blocked by #1383

Add a decorators = list() argument to the module() function and pass decorators to the server_args and ui_args. Revisit the documentation of teal_transform_module and teal_data_module and focus that it is clear:

• teal_data_module() is to create the teal_data during app run
• teal_transform_module() is to modify data, they can be used in two ways:
  • transformers: to modify teal_module's data input
  • decorators: to modify teal_modules's output objects