[Feature] Input text around param invocations. 

Currently there's no way to add text to component children. 

As an initial step in this direction I'm suggesting to be able to: 

```
<Component>
  add text {param} next to params
</Component>
```

This can just be a `template` property on the Invocation model, perhaps in tagged template style: ['add text ', ' next to params', invocationId] or something that suits.