Prepare tutorials for other platforms (e.g. windows)

Clonning ```flutter-tutorials```repository and opening some of clonned tutorial in VS Code, I need to run ```flutter create .``` command (with DOT in the end) to enable all available platform, e.g. windows.

## What is wrong:
- tutorial directory is not valid package name (starts with number and contains hyphen)
- package name in pubspec.yaml is not equal to direcotry name