Rework DB layer for better performance and enable indexes

[Frostman]

• [ ] bolt schema improvements
• • [x] bucket per type
• • [x] simplified keys w/o namepaces and kind in it, for policy objects key will return ns/name
• • [ ] use binary.LittleEndian.PutUint64 for version encoding
• • [ ] replace current key with "reference" that include kind, namespace and name
• • [x] deleted flag should be handled outside of DB layer, it's just a Versioned object with deleted field
• • [ ] do setting of new generation inside same transaction
• [x] add indexes support
• • [x] implement indexes primarily w/o using reflection
• • [x] support list / first / last indexes
• • [x] automatic index for versioned object to query last version
• • [x] get should use index for getting last version of the versioned object
• [ ] cover all parts of new DB layer with at least basic unit and integration tests
• [ ] encoding improvement
• • [x] separated codec w/o kind manipulation for higher performance
• • [ ] use god or message pack by default
• • [ ] codec benchmark to find best codec for DB