[ADD] Migration scripts for the project addon

Hi Sandy, I refactored the method that is shown in the highlighted code in this github thread. Unfortunately, I now realize that is not what you mean. It is simply context code, and you meant to comment on the very last line, which is the start of the update_alias_parent method :-( But the mapping of priorities is actually featured in 5 modules in 8.0, and I made the method simply generic so I hope it can stay.

About updating alias parent settings, I have my doubts. The settings self are a bit obscure, and they vary from model to model. Let's wait until other models are adapted to have a clear view of the common code.