Improve DB-schema migration robustness.

A migration should now be able to resume in some more cases after a
previously failed upgrade.
Merge pull request #554 from 4teamwork/deif-migration-robustness

Improve DB-schema migration robustness.
Update doc-properties when moving/copying documents.
Update DocProperties after document checkin/checkout.
Create journal entry when updating/adding doc properties.
Remove duplicate readme entries, improve readability.
Update history.
Merge pull request #551 from 4teamwork/deif-update-docprops

Update DocProperties for Documents that already have them.
Add utility method to generate an Oguid for an object.