Add core_ prefix to 2 db table names

[fyliu]

Fixes #497

What changes did you make?

• Added the "core_" prefix to 2 table names

Why did you make the changes (we will use this info to test)?

• It makes them use the same naming pattern as the other tables (starting with "core_")

Table names after the change

 public | core_project_affiliate_xref           | table | people_depot                                                                                         
 public | core_project_stack_element_xref       | table | people_depot                                                                                         

See issue description for the complete output and description.csv

Testing

• don't worry about the merge/migration conflict in the PR check. We'll fix that when merging the code.
• Just make sure the table names are changed and the tests still pass.
• To get all table names, refer to one of the note boxes in this guide.
• To start with an empty database, use the -v option in ./scripts/buildrun.sh -v