Check DB version before start and output human-readable message

After some period of non-update I run xenochain-validator and got:
```
xenochain-validator: CBOR encoding error: DeserialiseFailure 3 "Wrong number of fields: expected=6 got=5"
CallStack (from HasCallStack):
error, called at ./Thundermint/Store/SQLite.hs:180:18 in thundermint-0.1-3km53HaSeEXDEGt9wcLp4W:Thundermint.Store.SQLite
```

There is no information in this message about problems with DB :(

So I ask to add field "version" in DB and check it before start. If version is not supported, output message about this and path to DB.