flowable-modeler: Provide more informative error message when deployment fails?

When deploying apps from the modeler some error messages could be even more helpful.

For example when the deployment fails the modeler displays `Invalid Deploy result code: HTTP 500`

The server logfile includes a detailed error message with the reson why the deployment failed:

```
05:12:40,957 [http-nio-8080-exec-60] ERROR org.flowable.engine.impl.bpmn.deployer.ParsedDeploymentBuilder - Could not parse resource Test.bpmn
org.flowable.bpmn.exceptions.XMLException: cvc-datatype-valid.1.2.1: 'Test 2' is not a valid value for 'NCName'.
```

It could be helpful to propagate these errors to the modeler, what do you think?