[ticket/12786] Extend profilefield_base_migration.php class

If extensions authors will use profilefield_base_migration.php class as base class for creation of CPFs, the class need to be extended a bit.

At the moment there are two issues with it:

- It does not create entries for PROFILE_FIELDS_LANG_TABLE (as it can't know what fields to create).
- The migration is not "cleaning" the DBMS after purging the extension and leaves everything except the CPF column.