Sealed class

[glureau]

Exporting sealed class with KotlinJs make the code executable but not compliant with strict typescript rules. (The generated class is not abstract but with abstract fields for example, creating issues on typescript.)

https://youtrack.jetbrains.com/issue/KT-39193

We could generate an abstract class instead: the sealed is important for Kotlin side, but it has no class hierarchy limitation on the JS/TS word, so it's probably nothing more than an abstract class for the facade.

[glureau]

Released in 0.4.2