[z2005] Support loading tables with default filling into SQL-Loader

* Add special field markers to fill a column in SQLStorage with default values
* Add a safeguard to DBCStorage::EraseEntry, Add helper function DBCStorage::InsertEntry to store content

Note: If required similar adjustments to DBCStorage might be reasonable if required

(cleaned version of cedab61)

(based on commit [s1587] - bde8995)