Support custom distro-provided pages
This commit adds infrastructure for distros to provide their own pages placed in /var/lib/plasma-welcome-extra-pages/ (which is also distro-customizable in CMake) that will be shown in the wizard, right before the "Get Involved" page.
The readme file is updated with documentation regarding how to adopt it.
Fixes #7 (closed)
co-authored-by: Aleix Pol aleixpol@kde.org
Test plan:
Create /var/lib/plasma-welcome-extra-pages/ and place the following file in it, then build and run the app with this MR and go through all pages:
cc @apol