This is a generalization of the customwizard (using Json for its
configuration files since that is so easy to handle in Qt 5 and
since it is incompatible with the customwizard anyway).

It allows to define an arbitrary number of pages and generators to
generate the actual files.

Change-Id: I45a01cf7fb906701b627fa1471a898cad472f679
Reviewed-by: Daniel Teske <daniel.teske@digia.com>