Drop auth-file default path #420, Use click.prompt(), click_context testing

• Allow to pass any context object to define_click_context()
• auth: import top-level click
• auth: Replace getpass.getpass with click.prompt(hide_input=True)
• Use one option -af/--auth-file, AUTH_FILE_PATH context
  • Remove default auth file path for security reasons
• authentication cmd: stop reading default ./authfile