Metadata (json) fetch

[mariomatic]

Given a token address , we would need to fetch the json metadata from the uri field of the metadata account data.

Maybe implement metadataJson as a class?

[hoakbuilds]

This this may be a bit out of date but might come in handy, in that project I was deriving the PDAs for the Metadata Accounts and then getting the actual Metadata from Arweave and wrapping it all into a single class in the end

[mariomatic]

implemented simple fetching of json as string for now #36