lib-lee: MoodleManager (legacy)

A wrapper for mod_xr. To be replaced with a lighter Moodle mod that communicates with lxr, keeping the back-end logic in lxr.

It uses Moodle's moodle-mod_xr web services to create, read, update, delete activity models, to create, read, update, delete media assets used by content augmentations, and to provide search functionality for the activity list (including paging through it).