Updated schema migration script for DEV24->DEV25

Rollout to my deployment platform identified an
issue with sequence allocation. Not sure why this
wasn't flagged at DEV24, but may be down to Hibernate
version change in DEV25.
Added "purge anonymous data" manager action
Further tweak to HEAD~2

I now realise the primary key generation issue when
deploying to dev was down to the sequences in the DB
being out of sync with the @SequenceGenerator annotations.

These need to be manually synced, which I have included here.
I expect to make some further tweaks for the next snapshot.
Minor changes to @SequenceGenerator values

In light of issue noticed last time, I've changed the
increment values to more sensible values.