Alertify utility to log $http errors

Every time we use `$http` to make an API request from the frontend, we need to alert if it fails.  That's actually a little messy: `alertify.error("Failed getting job logs: " + data.data.error.name);`

Instead, something like this would be great:
```
$http.get(..)
.then(function (data, status, headers, config) {
}, alertify.http_error_handler("Failed to get job logs"))
```

Whether to embed this in `alertify`, make it an Angular provider, or what needs a bit of thought -- I don't mean to imply an answer to that question here.