[bugfix] Enable test_detect_site for wikichristian.org
[bugfix] Enable test_detect_site for wikichristian.org

- SiteDetectionTestCase.test_detect_site() failed for wikichristian.org.
  I found several newlines on top of the json file and a Byte Order Mark (BOM).
  Removing them solves the problem.
- Also add a __repr__ for MWSite so show this repr string instead of the
  generic <pywikibot.site_detect.MWSite object at 0x032D06F0>. Now we get
  the class Name with the new url where the json is fetched from

Bug: T128992
Change-Id: Ib8b4c0d5dbf645d4984d26f5ac35f8f98e1ca418

npdoty/pywikibot,PersianWikipedia/pywikibot-core,hasteur/g13bot_tools_new,hasteur/g13bot_tools_new,magul/pywikibot-core,Darkdadaah/pywikibot-core,happy5214/pywikibot-core,wikimedia/pywikibot-core,jayvdb/pywikibot-core,wikimedia/pywikibot-core,hasteur/g13bot_tools_new,jayvdb/pywikibot-core,npdoty/pywikibot,magul/pywikibot-core,happy5214/pywikibot-core,Darkdadaah/pywikibot-core