This allows work on the UI to be started.

Given an item in the context tree (a specific course or course module, etc), we need to be able to set its category and purpose and store this in the Data Privacy tool. This issue is about the back end only.

Note: Categories and purposes are user-configurable - see MDL-61362. Do we link these or copy these when storing the relationship between contextid/component and purpose/category?  - This is up for discussion on this issue.