JsonWizard: Add a customizeable page

Add a way to define custom pages with checkboxes, lineedits, etc.
on it.

Change-Id: I012109eabf00a12abc67ae34514d139b7cd7cf0d
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
JsonWizard: Replace JsFileWizard with a JsonWizard

Change-Id: I4da3485ed83fda7f17f3fa9a1f3d59bfabb7ea4d
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>