Fix tutorial error and update API reference

[ZergLev]

Description

Minor fix and updates to 'Tutorials' and 'API reference'.

• 'API reference' claimed "wrappers" are a parameter of both classes Pipeline() and Service(), but instead there are "before_handler" and "after_handler", now updated.
• For the above reason, replaced term "wrapper" with "extra handler" where appropriate within both tutorials and docs. (user guides required no changes)
• Similarly and for the same reasons, references of "services" from class Pipeline() changed to "components" both within docs and tutorials. (user guides required no changes)
• In tutorial Script/Core:4.Transitions comments had wrong order of transitions, now fixed.

Checklist

• I have performed a self-review of the changes

To Consider

• In dff/stats/utils.py there is a function called get_wrapper_field(), but wrappers were changed to extra handlers, I think. Is this intended?
• Currently, there are no explanations or links to API within the tutorials as to what ExtraHandlerBuilder and ExtraHandlerFunction objects are.
• Search for references to changed entities in the API reference/tutorials/guides