Fix capitalization in ApiQueryBase::titlePartToKey()

ApiQueryBase::titlePartToKey now allows an extra parameter that
indicates the namespace in order to properly capitalize the title part.

This allows list=allcategories, list=allimages, list=alllinks,
list=allpages, list=deletedrevs and list=filearchive to
handle case-sensitivity properly for all parameters.

Bug: 25702
Change-Id: Iaa5a71ec536f3716f54bc84b39f645545dfd8660