Data migrtation improvements

[kirillvasilenko]

1. Fixed the after-migration string and set validation. Now it takes into account Classic Xodus "broken" strings.
2. Fixed working with blobs. Some of the Orient methods add random bytes to blobs (a bug in the database), so now we use another method.
3. Improved the after-migration validation performance.
4. Made the migration and validation logging more frequent and clear. Added progress to it.