Governance module for generic voting procedure by Trustees

[ashcherbakov]

We need to implement a governance module similar to https://github.com/cosmos/cosmos-sdk/tree/master/x/gov which can be used as a general way for propose-approve by Trustees approach.
Propose-approve approach is used in multiple modules, so we need to re-factor that modules to use the transactions from the governance module instead of custom Propose/Approve transactions.

Acceptance Criteria:

1. Create x/dclgov module. It can be based on https://github.com/cosmos/cosmos-sdk/tree/master/x/gov, but we need to get rid of staking and tokens.
   • Implement a generic voting (approval) mechanism in dclgov.
   • Be able to specify roles (Trsutee by default) and min number of approvals for every Proposal
2. Apply the new voting mechanism to the following modules (instead of the current custom approvals):
   • dclauth
   • pki
   • dclupgrade
3. Support negative votes (against the proposal)
4. Support removal of pending entities
5. Add unit tests
6. Add integration tests