Added basic implementation to TokenCloudCredentials without support for token renewal.
Added support to refresh credentials in CloudCredentials
Changed RefreshServiceClient to be async to support long running refresh operations
Rolled back RefreshServiceClient method
Added ability to specify token type
Added null check
Removed extra new line
Updates based on the code review
Fixed copy-paste errors in comments
Merge branch 'dev' into token-credentials
Merge pull request #385 from stankovski/token-credentials

Basic implementation of TokenCloudCredentials