fix. extend namespace

[nyufeng]

Description
Pages extends CodeIgniter\Controller replace to Pages extends \CodeIgniter\Controller
CodeIgniter\Controller class in root namespace

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[jim-parry]

@lonnieezell What convention should we be following?
Some of the examples in the user guide use namespaces (App\Controllers) while others don't.
Some extend "\Codeigniter..." while others extend "CodeIgniter...".

[lonnieezell]

That's because, in part, I didn't think it was necessary to repeat the full structure every time, but maybe that is a better practice.

• All controllers should have the App\Controllers namespace
• I would always have a use statement above the class: use CodeIgniter\Controller
• so only ever have to MyClass extends Controller

[jim-parry]

There are a bunch of instances where this needs to be corrected, and following Lonnie's suggestion, not the path taken by this PR. I am closing this, and will make a sweep of the user guide looking for these changes.
Thank you @Instrye for bringing this to our attention :)