Overhaul application adding process

[omeritzics]

The current application adding process is quite unordered, complicated, and not user-friendly.

My goal is to:

• Unify all the source setting code into source_provider.dart
• Simplify the application adding process by moving expert-options (such as Shizuku features and regEx options) to a new 'Advanced' section.
• Reorder the options in the application adding procedure.
• Transform the source search dialogue into a full screen
• Make it clear to the user in which step they are, by adding a progress indicator.
• Let the user edit key properties also after adding the application.

These steps are not final and there is still planning required, but this is, I hope, where Updatium is going.
Any ideas are welcome.