standardize nowcommons.py

- NowCommonsDeleteBot extends pywikibot.Bot

- pass options to the bot class constructor
  instead of using global variables

- BREAKING: the '-autonomous' argument has been replaced
  with the standard '-always'; the former is provisionally
  retained for backwards compatibility

- replaced NowCommonsDeleteBot.urlname() with Page.title(asUrl=True)

- the argument parsing has been optimized

- replaced ImagePage.fileIsOnCommons() with ImagePage.fileIsShared()

- pywikibot.inputChoice() always returns the short variant, lowercase

Change-Id: I1cc6b5734237d143c8100f3c26c20d78c36924c6
Merge "standardize nowcommons.py"