Refactoring and improvements

[tg666]

• Add more abstraction (interfaces for classes Notifier, Notification, NotificationBundle etc.)
• Create the only one Component with different templates only
• Reimplement storages better. Storages must be configurable in neon
• Add a Database (Doctrine) storage with default an Notification entity
• README
• Tests

[jelen07]

Inspiration

• https://symfony.com/doc/current/notifier.html
• https://laravel.com/docs/8.x/notifications

Requirements

• Unify API when working with notifications (sending SMS vs setting flash message, form/form input error, etc.)
• Use channels
• Support of flash messages, toasts, SMS, e-mail, Slack, logger, database notifications, console output, etc.
• Translations - system (UI) and user's (e-mail, ...)

Set roadmap and priorities.