Fix migration restoreReferencesOrder removes references

The restoreReferencesOrder iterates over all UIDs in obj._relatedItems
to recreate obj.relatedItems. That way the references from obj._backrefs
are removed.

The fix removes restoreReferencesOrder and adds a beforeChange_relatedItemsOrder
method to fhe ReferenceMigratror class. That method stores Archetype relations as
target uids on the old archetype object to restore the order later.
Because all relations to deleted objects will be lost, we iterate
over all backref objects and store the relations of the backref
object in advance.
updated CHANGES.rst
Migration for DX-based plone.app.event objects
Migrate both PATCT and PAE (AT) Events. Use default_timezone for PATCT
Also migrate exclude_from_nav
don't break if portal_atct is absent
we need a new way to configure the image types, but for now use Image by default
Actually test migrate_events finds appropriate objects
Add migration step for 1.0 p.a.contenttypes Events too
Update comment, it really is a 1.0 object now
Use assertEqual when comparing numbers.
Merge pull request #94 from plone/migration-steps

Add more migration steps
add atomatic upgrade step
also make sure plone.app.event's default profile is installed
Revert "also make sure plone.app.event's default profile is installed"

This reverts commit 719b9611b8581529f39463d1ad15e0edd700a932.
Revert "add atomatic upgrade step"

This reverts commit 83e193afafe39ed98e9b942717911c902eed782d.
Merge branch 'master' into fix_migration_restore_references_order_removes_references

Conflicts:
	CHANGES.rst
small hint for developers
Merge pull request #84 from plone/fix_migration_restore_references_order_removes_references

Fix migration restoreReferencesOrder removes references
Remove test profile, define in helper method instead