Update blob to v0.19.0
Update commit to v0.19.0
Update config to v0.19.0
Update Database and DatabaseBackend to v0.19.0
Implement DatabaseObject
Update Index and related to v0.19.0

Note that a rework of IndexEntry is needed.
Some memory leak or corruption can occur.
Upgrade References and related to v0.19.0.

Not completely done yet.