Extract walletcore (separate repository)

[andreibancioiu]

• Removed walletcore and crypto folders. They are now located at: https://github.com/ElrondNetwork/elrond-sdk-erdjs-walletcore.
• Added erdjs-walletcore as a dev-dependency only (for integration tests).
• Added a "boundary adapter" to resolve the impedance mismatch between erdjs-walletcore (and others) and erdjs.

package-lock.json generated with node v16.14.2 and npm v8.5.0.

For review:

• make sure you have latest nodejs (LTS 16.x).
• clone the repository locally, checkout to extract-walletcore
• remove the file package-lock.json
• run npm i
• assert there are no changes to commit