Adds migration that fixes old journals.

Parent ids in planning element journals remained the same during the
earlier journal migrations and need to be fixed. This migration works
for postgres only.
Merge remote-tracking branch 'opf/feature/rails3' into fix/migration-of-legacy-planning-element-journals

Conflicts:
	doc/CHANGELOG.md
Adds missing method.
Merge remote-tracking branch 'opf/feature/rails3' into fix/migration-of-legacy-planning-element-journals

Conflicts:
	doc/CHANGELOG.md
Merge pull request #673 from opf/fix/migration-of-legacy-planning-element-journals

Adds migration that fixes old journals.