Formal way to take in token for slideUtil

[birm]

In secure deployments, we need a token to upload slides. Thus, slideutil needs a better way to take in token. This is likely a good opportunity to make it take in arguments for filepath too.

[tani-dubey]

The upload token is currently being printed to stderr from continue_file( ) due to a debug statement (print(token)) . I can submit a PR to remove the print or mask the token in logs to avoid leaking sensitive authentication information.