feature/Create migration for redeploying District.sol and DistrictFactory.sol

[madvas]

In order to keep our existing districts on blockchain, we'll need truffle migration for partial redeployment, after the Snapshot Integration merge.

Truffle migration file should:

• deploy District.sol
• deploy DistrictFactory.sol
• call setFactory method on existing :district-registry-fwd contract address with the newly deployed DistrictFactory address

Additionally we should create another truffle migration file, which calls setFactory with the old DistrictFactory.sol address (address can be hardcoded), setting it to false. So old factory contract will be disabled once we test our new deployment in production.

[ginesdt]

Registry.sol should also be deployed, shouldn't it? The signature of fireDistrictConstructedEvent() and DistrictConstructedEvent changed as part of the snapshot integration.
New Registry.sol should be constructed using existing :district-registry-db.
Finally, a call to setTarget on :district-registry-fwd would be also needed to point to the new Registry.sol deployment.