Create "state" and "cache" folders

[webmaster128]

For a node operator it should be obvious which disk content belongs to the state of the blockchain and what is caching data that is re-generated on demand. This distiction should also be more prominent in this code base. The future layout should look like this

base/
├── state/
│   └── wasm/
└── cache/
    └── modules/
        └── v1/

For state sync it will be necessary to copy the state, but not the cache: CosmWasm/wasmd#478