Create new structured format for Playground bundle

[hrajchert]

We should improve the structure of the Exented bundle to include the following:

• A version of the bundle to allow backward compatibility
• The JSON representation of the Extended contract
• The Metadata
• Maybe the Source code if it's pure Marlowe (we can avoid it and pretty print it from the JSON)
• The Source code and an optional Source Map (targeting the pretty print or the JSON?) if it is generated from Haskell/JavaScript

We should also remove the empty playground.marlowe.json file which is currently used only to distinguish Marlowe gists from other gists and provide a tar file instead.

[hrajchert]

After talks with @paluh for this issue, the initial implementation will:

• Not contain source map between Sources to Target
• Will merge the playground.marlowe.json with the metadata
• Will add Bundle version, Core/Extended version and Haskell version/TypeScript version when applicable

We still need to define if we include the JSON representation of the Extended Marlowe or if we leave that for the Executable bundle that will be used together with marlowe-cli and should be a different issue. My thinking is that if we agree on separate a playground bundle from executable bundle, then there is no need for us to have the JSON representation here, and only the textual representation if the source is plain Blockly/Marlowe.

[paluh]

Thanks for writing that down @hrajchert. I think that I'm going to stick to the source only bundle for this case.