Add Move Playground JS Library

js-move-playground wrapper Move Playground by Pontem as javascript library for browser. Developers can use it to build their own Move Playground.

Thank you for the contribution, and following guidelines such as descriptive commit messages @locfortyfour :+1: However, the newest commit introduces more problems: the ToC does not need to be changed, since you add only one entry, and not a category. The only change needed to the original commit is to change javascript to JavaScript (Awesome list style guidelines require using proper brand naming).

@locfortyfour Thanks! Almost there: Javascript is still not JavaScript (see above), hence failing lint. Once this is fixed, I will merge this :+1: (force push the change as you did with the last commit)

@locfortyfour Thank you, merging this! :+1: