fix(@embark/core): Disable swarm if URL can’t be determined
fix(@embark/core): Disable swarm if URL can’t be determined

If the storage config is set up in such a way that a URL for swarm cannot be determined, the swarm module will exit early.

For example, if the storage config looks like:
```
available_providers: ["ipfs", "swarm"],
    upload: {
      provider: "ipfs",
      host: "localhost",
      port: 5001
    },
    dappConnection: [
      {
        provider:"ipfs",
        host: "localhost",
        port: 5001,
        getUrl: "http://localhost:8080/ipfs/"
      }
    ]
```
Then there is no way to determine the swarm URL as neither `upload` nor `dappConnection` specify a provider with `swarm`. If this is the case, the swarm module will exit in it’s constructor.

Add a warning message in the console for the users.

iurimatias/embark-framework,iurimatias/embark-framework