Add function to get a message signed

Expose a new function to be consumed from other apps to get a message signed:

Here's how the builder is currently doing it, we should transform it to `async/await` and define the parameters to make it generic.

```
const signature: string = yield call([provider, 'request'], {
method: 'eth_signTypedData_v4',
params: [from, msgString],
jsonrpc: '2.0'
})
```