GitLab

This reverts commit 229ae27c.

Fixed the writer so that doesn't create an empty
folder if there is no data to export.

Adds another level of interfaces extending data_provider, namely
core_data_provider and shared_data_provider. Makes it easier to locate
components providing data to core, and the subsystem's manager.

Thanks to Gareth J Barnard for this suggestion.

AMOS BEGIN
 CPY [userpreferences,grades],[userpreferences,moodle]
AMOS END