display in-progress build messages

When you compile a project on the command line, you often see messages like this scroll by:

```
Compiling lexical-core v0.4.
Compiling atty v0.2.13
Compiling termion v1.5.3
```

These are nice indicators to the user that the build is in progress. We should display these messages in the front end somewhere.

The json format of these messages (as far as I can tell) is that they have a `"reason": "compiler-artifact"` key-value pair:

```js
{
"reason":"compiler-artifact",
//...
}
```

We can detect these fairly easily, the question is how, where, and when to display them on the front end. Suggestions welcome!