[ARCHETYPE-559] Invalid package names are not rejected during archetype generation.

**[Cameron Hudson](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cameronhudson8)** opened **[ARCHETYPE-559](https://issues.apache.org/jira/browse/ARCHETYPE-559?redirect=false)** and commented

Steps to replicate:

`$ mvn archetype:generate`

I then entered
* `1313` for the quickstart archetype.

* `8` for quickstart archetype version 1.4.

* `info.cameronhudson.18655` for the groupId

* `lab1` for the artifactId

* `1.0` for the snapshot version

* `public-recommendation-service` for the package name

* `Y` for confirmation

This successfully creates a project, even though the package name is invalid.

Attempting to run mvn clean install results in misleading compilation errors:

```
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /Users/cameronhudson/Repositories/CMU/18-655_Lab_1_Public_Recommendation_Service/lab1/src/main/java/public-recommendation-service/App.java:[1,8] expected
[ERROR] /Users/cameronhudson/Repositories/CMU/18-655_Lab_1_Public_Recommendation_Service/lab1/src/main/java/public-recommendation-service/App.java:[1,15] class, interface, or enum expected
[INFO] 2 errors
```

 

Expected behavior:

Inform the user that the package name is invalid (ideally, explaining why it's invalid) and present the prompt again.

---
No further details from [ARCHETYPE-559](https://issues.apache.org/jira/browse/ARCHETYPE-559?redirect=false)

Start with the prompt flow reached by `mvn archetype:generate`, focusing on how the package name is accepted and how invalid input is handled. Reproduce the case with `public-recommendation-service`, then run `mvn clean install` on the generated project; done means invalid package names are explained and the prompt is shown again.

Written by the indexing model from the issue text.