Add skeleton of upgradedatabaseFormatVersion3()
Add important TODO/FIXME to upgradedatabaseFormatVersion3()
Fix FreenetURI leakage in class (Own)Identity:
- The following commits will implement WebOfTrust.upgradedatabaseFormatVersion3() which will delete the leaked objects.
- Bugtracker entry: https://bugs.freenetproject.org/view.php?id=5964