Rollback changes on route handler crash

Overview

According invariant no.5 we should revisit the behavoir on handler crash.

Current state

On handler crash we just return the error, but do not rollback/revert any appied changes to database/blockchain.

Improvement

1. SQL-chain: I think we can do it via database features;
2. File-chain: we need to add rollback to Pheix::Model::Database::Filechain module;
3. Blockchain: tricky thing, but I think if we can implement it for File-chain, we will be able to apply the same implementation to Blockchain.

Notes:

• consider performance and runtime speed for Blockchain;
• consiter this feature as configurable via the settings.