Help: Allow use of stripped down WebKit as help browser

Change-Id: I9571b70b6eb3c6e27adf482ea24049d66244bbc7
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/help/help.pro

 QT += help network printsupport sql
-!isEmpty(QT.webkitwidgets.name): QT += webkitwidgets webkit
+!isEmpty(QT.htmlviewwidgets.name): QT += htmlviewwidgets htmlview
+else:!isEmpty(QT.webkitwidgets.name): QT += webkitwidgets webkit
 else: DEFINES += QT_NO_WEBKIT
 
 INCLUDEPATH += $$PWD