WIP: New pre-deploy contracts

[DarianShawn]

Description

1. This PR import two new pre-deploy contracts, Bridge and Vault.
   Bridge contract is used for dogecoin blockchain crossing.
   Vault contract is used for system reward collection and community profit sharing (T.B.D.).

2. Add an owner to Staking contract, who in charge of validator authorizations.
   The owner would return rights to the community in the near future.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Different genesis means re-deployment of network or hard fork. Re-deploy network would be a better choice for now.

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

1. Set up a local network of 4 nodes, which uses a Genesis sharing the same owner of all system contracts.
2. Try deposit, withdraw token from Bridge contract.
3. Check out the ValidatorSet on Staking contract.
4. Add and remove validator, using the owner authorization.

[abrahamcruise321]

LGTM