Clean up choices for v1 to v2

Some decisions were taken in the migration process from version 1.11.* to version 2.0. Here is a list for review by admins of large portals where these decisions might have a notable impact.

Features included late in 1.11.x branch

We have split 2.0 from the 1.11.x branch around version 1.11.10, so all features added after this date are likely not present in Chamilo 2.0. The database structure for those features will be there, but some elements of the interface might be missing. We will work through most of those missing features in future versions of Chamilo 2.*, but integrating them all would have postponed the release of 2.0 by another 3 years or so, so we had to take a (hard) decision.

gradebook_category.parent_id

Some data in 1.11's gradebook_category table were allowed to have a parent_id pointing to a non-existing gradebook_category.id. For consistency reason, we have decided to remove such gradebooks, so if any gradebook_category record points to a non-existing parent_id, it will disappear completely after the migration (it would probably not have appeared in 1.11.x's interface anyway). If you want to avoid this, make sure you go and edit parent_id fields (set them to NULL, for example) before you start the migration.

You can check for the existence of such records with the following query:

SELECT * FROM gradebook_category WHERE parent_id IS NOT NULL AND parent_id NOT IN (SELECT id FROM gradebook_category);