Support data downloading/uploading

[jeserkin]

Mainly issue is regarding -> https://jmap.io/spec-core.html#binary-data
In session response we have a bunch of different URLs including

{
  "downloadUrl": "http://localhost/download/{accountId}/{blobId}/?type={type}&name={name}",
  "uploadUrl": "http://localhost/upload/{accountId}"
}

So as far as I can tell, what can be done on jmap-client-ts level is:

• return URL with accountId replaced, since it is present in session response as well.
• For upload, there could be a type definition for response as mentioned here https://jmap.io/spec-core.html#uploading-binary-data
• Also for upload, there could be an entire method present, that would allow data upload. End-user should provide only body value, e.g. Blob

If there are any other suggestions on how to proceed with it, then I would love to hear about it.