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

[PavelPZ]

Clonning flutter-tutorialsrepository 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