Add Simulator for EthermintApp

[fedekunze]

Proposal: Add simulation support for all modules but x/evm

Use case: Allows to fuzz test an SDK application and detect bugs before merging PRs (if integrated with CircleCI/ GitHub Actions).

Recommended readings:

• https://docs.cosmos.network/master/using-the-sdk/simulation.html#simulation-commands
• https://docs.cosmos.network/master/building-modules/simulator.html

ToDos:

• add tests
• Makefile
• add to CircleCI

Requests may be closed if we're not actively planning to work on them.