AvailableTaskPagesModel groups projects by data source
Summary:
This way we get some grouping of the projects which is very welcome and
the right way to do it for projects. Obviously requires to adjust the
feature tests quite a bit since it impacts all the page management
tests.
Reviewers: bensi, dfaure, franckarrecot
Differential Revision: https://phabricator.kde.org/D7052