Gather all soft-disabled uploads wikis in one config item

Greatly simplify so called soft-disabling of local uploads for configuration
to be more readable and reduce mistakes. The most common setup is achieved
by an ad hoc "commonsuploads" group and only deviations need be explicit.
No changes are made to the actual configuration in this patch, other than
fixing some obvious, minor oversights caused by the former un-readability.

They are all listed below.
* zhwikinews: redundant config removed, it has $wgEnableUploads false.
* guwikisource: current config completely wrong, bug 36345 asked upload
  disabled but it was only for "user" so "autoconfirmed" can upload since
  the global default changed; they have a local hack, now do it properly.
* Some wikis are added to $wgUploadNavigationUrl, for which we previously
  forgot to follow the code comment which says "make sure to make an entry
  for $wgUploadNavigationUrl as well" when the uploads are not going to be
  used locally. No ?uselang hacks, we have ULS now for registered users.
** jawikiversity, ukwikivoyage: no local uploads for 5+ years, help users.
** guwikisource: another oversight they didn't ask, as above.
** iswikibooks, iswikiquote: bug 11317 and bug 11318 asked to do changes
   as established by local discussions/guidelines, which do mention
   sending everyone to Wikimedia Commons for uploads. Let's do it.
** itwikivoyage, itwiktionary: it* projects traditionally add anyway, in
   the toolbox, a link to upload to Commons, via a local hack. Do it
   properly for the two which soft-disabled local upload.

Also copied one comment from groupOverrides to groupOverrides2.

Change-Id: I248fa7b98a8a0eea943c6643d1bf9c2ed36296b8