[prep-release-3.1.0-RC5] Add migration for 3.1.0-RC5
Merge branch 'develop-ascraeus' into develop

Conflicts:
	build/build.xml
	phpBB/includes/constants.php
	phpBB/install/schemas/schema_data.sql
	phpBB/styles/prosilver/style.cfg
	phpBB/styles/subsilver2/style.cfg