Do not allow periods in a project name.

This causes issues with the way we export information to `window` in
`app/index.html`. For example (assuming a project name of
`zomg.awesome`):

```javascript
window.Zomg.Awesome = require('some-test/app')['default'].create(ENV.APP);
```

Which will obviously blow up because `Zomg` is not an object.
Merge pull request #927 from rjackson/disallow-dots-in-project-name

Do not allow periods in a project name.