-quiet option for noreferences, code cleanup

- implement the hidden -quiet option to prohibit verbose output
- use NoReferencesBot.site attribute instead of getting Site object
  over and over again
- use site.code instead of site.lang
- simplify inputChoise
- use page.text instead of page.get()
- use page.save() instead of page.put()
- return from method silently

Change-Id: I089625044be4a1866aeb6d42027b661ab316de1d
Merge "-quiet option for noreferences, code cleanup"