[IMPROV] Enable new watchlist parameters (MW 1.16+)
[IMPROV] Enable new watchlist parameters (MW 1.16+)

- improvement of Page.save method to enable all values for api
  watchlist (including "preferences" and "nochange").
  site.editpage() and api already use it.
- rename Page._save parameter "watchval" to common "watch". The
  internal _save method should never be used outside, so the
  renaming shouldn't care.
- backward compatibility for boolean watch parameter

see also https://www.mediawiki.org/w/index.php?title=API:Edit#Parameters

bug: T98830
Change-Id: Icf482b888829495e76813532f28da6bbf0525891

Darkdadaah/pywikibot-core,hasteur/g13bot_tools_new,icyflame/batman,h4ck3rm1k3/pywikibot-core,happy5214/pywikibot-core,npdoty/pywikibot,jayvdb/pywikibot-core,VcamX/pywikibot-core,wikimedia/pywikibot-core,npdoty/pywikibot,emijrp/pywikibot-core,xZise/pywikibot-core,hasteur/g13bot_tools_new,hasteur/g13bot_tools_new,jayvdb/pywikibot-core,trishnaguha/pywikibot-core,smalyshev/pywikibot-core,darthbhyrava/pywikibot-local,wikimedia/pywikibot-core,Darkdadaah/pywikibot-core,TridevGuha/pywikibot-core,PersianWikipedia/pywikibot-core,happy5214/pywikibot-core,magul/pywikibot-core,valhallasw/pywikibot-core,h4ck3rm1k3/pywikibot-core,magul/pywikibot-core