Task 1856935
Currently, if installing a module's demo data fails (because the
module was uninstalled and some were left over and can't be
reinstalled, or because they're broken, or…) the installation of the
module fails and further installations are skipped (?).
Since demo data are non-essential (though required to run tests),
rather than fail everything if they fail just roll them back and
notify the user.
This change generates a warning log *and* shows a notification popup
to the end user.
Xavier Morel
e891313810