Port PikaOS Apps to otter shell

This should yield much better performance and customizability than the current GTK4 stack, it also makes us safe from any unwanted lockdowns that GTK might implement in GTK5.

should also make all our apps consistent with the upcoming "PikaOS Store"

Currently ported applications:

• Welcome App
• First Setup
• Device Manager
• Update Manager
• Kernel Manager
• Installer