Use datastore to persist matching results

[hodlbirb]

The following functionallity is needed for the service to be functional:

• Persist in the datastore the processing status for every incoming order as a special flag to destinguish orders that have been already handled by the matching engine which later will be used for recovery procedure
• Pull open orders with processing status from the datastore which will be used only once for recovery
• Atomically insert matching transaction between source order and distanation order (later can be done as bulk insert for multiple matched distanation orders)

[hodlbirb]

#5