Deals watcher

[kostysh]

When the Deal event is emitted in the Stays contract lpms-server must catch this event and check the availability of the associated space.

This issue is blocked by windingtree/stays-contracts#10

• If the availability of the space is less than booked in the deal this deal must be declined immediately. Timeout between the Deal event and decline transaction must be no longer than the timeout configured in the Stays smart contract (confirmation timeout of the state machine). This issue is blocked by State machine stays-contracts#10
• If the availability of the space is enough the watcher must decrease the availability value in the database by the value of the deal
• Implement tests for the new feature