QskDialog with callbacks

[uwerat]

For applications, that do not want ( or can't f.e WebAssembly without Asyncify ) to use recursive event loops we need to have an API, where the return value is accessible using a QskFunction parameter.

Something along those lines:

qskDialog()->question( "Really ?", QskDialog::Yes | QskDialog::No, []( QskDialog::Action action ) { ... } );