For KCM modules, clicking the "Help" button when khelpcenter isn't
installed should open the corresponding documentaion for that module
at docs.kde.org; for example with the Fonts KCM, the "&application="
part of the url should be "&application=kcontorl/fonts".

See D27518 for more details.

Thanks to ltoscano for fixing docs.kde.org to make "&application=kcontrol/<module name>"
actually resolve to the correct url path.

• make && ctest
• building systemsettings after applying D27518, make sure khelpcenter isn't available on the system, then open the fonts KCM and click "Help" the relevant page at docs.kde.org should open
• in systemsettings from its menu open the "Systemsettings Handbook", it should open the relevant page at docs.kde.org