Dummy webwidget

Hi @cgilles @mqualmann , Is this a good way to fix compilation with Qt6? I am planning to first fix all WebEngine/WebKit code like this and then try to link targets with Qt6.

There are two dummy widgets

• DNoWebWidget based on QLabel
• DNoWebDialog based on QMessageBox

Both have some empty functions and signals to compile successfully.

If No web module is found, code containing Web* functions won't be compiled and client code is wrapped with Dummy code displaying warning.

• WelcomePageView (DNoWebWidget)
• inatbrowserdialog (DNoWebDialog)
• wsauthenticationpage (Not built in digikam)
• vkontake_authenticationdialog (DNoWebDialog)
• webbrowserdialog (DNoWebDialog)
• backendgooglemaps (DNoWebWidet)