v2 API requires changes to authorization flow

[StraightfaceStudios]

In regard to ../b2/response/B2AuthorizeAccountResponse.java:

In v2 of the API there can now be application key pairs that have permission to only ever read specific buckets.

"Most of the API calls that deal with buckets or files use a bucketId to identify a bucket. But, when using an application key that restricts access to just one bucket, you can't use b2_list_buckets to list all the buckets.

When there is a bucket restriction, the bucketId and the bucketName for that bucket are in the response from b2_authorize_account in the allowed section. You can then use that bucketId in all of your later calls."

https://www.backblaze.com/b2/docs/application_keys.html#usingRestrictedKeys

As a result there needs to be a new attribute in the b2client object that includes a list of "Allowed" buckets. The response from Backblaze now looks like this:

  "allowed": {
         "bucketId": "****",
         "bucketName": "AAABCC",

And add some sort of functionality like b2AuthorizeAccountResponse.getAllowedBuckets()

Similarly .../b2/request/B2ListBucketsRequest.java will need to be extended to avoid the error scenario where listing buckets results in a permission error even though the account can list specific buckets.