Migrate Admin contract to v0.4.0

Summary

In order to perform contract instantiations or migrations, these need to pass through governance since the Nolus network
is a semi-permissioned blockchain. This proposal aims to migrate a new version of the Admin contract on the Nolus Pirin mainnet. This update seeks to introduce the following:

• Allow the Admin contract to support multiple decentralized exchanges (DEXes).
  
• Introduce a DEX admin address which would be allowed to instantiate and register new Protocol contracts into the Admin but not to migrate them.
  This is a prerequisite to the migration of the remaining contracts to v0.4.0. The complete changelog can be seen in the Github release v0.4.0. By voting YES on this proposal, you agree to migrate this new version of the Admin smart contract.