Restructure things to allow more kinds of migrations.
Fix tests.
Only set up old conversations if needed.
Implement applies_to for batch separation.
Implement the top-level logic for the tag separation migration.
Copy batches.
Don't implement default .applies_to().
Fix help text for separate-tag-batches migration.
Add test for unknown migrations.
Re-write which conversations batch fixing applies to.
Avoid use of built-in name 'list'.
Avoid generating a list of all conversations.
Add missing fullstop.
Fix test names.
Remove unnecessary setting of delivery_tag_pool and delivery_tag in tests.
Add conversation with multiple batches.
Add conversation with no batches.
Separate out tests for fix-batches.
Merge branch 'feature/issue-601-conversation-batch-splitter' into develop
Merge branch 'develop' of github.com:praekelt/vumi-go into develop