WebComponent build does not work

[teampolyglot]

The ideal API we want for this library is demonstrated in https://github.com/learn-awesome/flashcard/blob/master/webcomp.html

However, this currently does not work. I couldn't figure how to make slots work well. Even the fc-flash-card component with <fc-question> and <fc-answer> nested children elements does not work.

This needs to be fixed for easier usage of this library.