Consider supporting non-graceful shutdown in Kura

[dima74]

Consider a non-graceful shutdown occurring to Iroha in the middle of Kura saving data to disk (for example, due to power loss or being killed by the OOM killer). In this case, the data on disk might be in an incomplete or inconsistent state, leading to data corruption. This can be solved using custom write-ahead logging in Kura or crates like this.