fix: Steps in tutorial that were outdated

[jdurand-teclib]

This fix proposition aims to change some parts of the tutorial that are outdated. The changes are mostly about some files that are no longer needed due to new templates or automatic actions made into GLPI's core, some parts of the code that now work differently, or some code pieces that were no longer passing the linters.

Here is a sum up:

• In the "Common actions on a object" part:
  • Removed the instruction to create the superasset.form.php file, as standard CRUD actions are automaticaly handled by CommonDBTM class. The example content of the file remains in the doc, so the user can see what it would look like if he needed to create a file to handle specific actions.
• In the "Hooks" part:
  • The "MENU_TOADD" hook was not documented in the hooks page.
  • The hook example for the ITEM_ADD was using an array of parameter, but this hook is called with an item as parameter, so the callback method was not reached. I updated the code to make this hook called with an item as parameter.
• In the "Importing libraries (Javascript/CSS)" part:
  • The second exercise was asking to create a button that already exists. I updated it to make simply change the appearance of the button.
  • The tutorial was asking to create a file named "ticket.js.php", but this file naming practice is no longer at use in our coding standards. I changed the file name to "ticket.js"
  • The provided template for common.js and ticket.js was not passing the ESLint, during the CI jobs. I updated it to make it pass the linter.
• In the "Notifications" part:
  • A code template was making the user display a "Submit" button in the method "showMassiveActionsSubForm", which is no longer required, as the template in which this template adds content already displays a Submit button.
  • A warning about the setup of a SMTP server was displayed, recommanding to install mailhog or mailcatcher. This warning is no longer needed, as the docker environment provides a mailpit already setup.

[SebSept]

Thanks for contribution :)
I did not run the code.
The comment about mailing utility is needed for me.

(and yes a doc about docker is needed too, but that's another work).