Grunt fails if project name is malformed

```
>> Tracing dependencies for: node_modules/almond/almond.js
[Error: Error: Parse error using esprima for file: /trabajo/collective/test_generator/js/bundles/bundle.js
Error: Line 19: Unexpected identifier
at /trabajo/collective/test_generator/node_modules/grunt-contrib-requirejs/node_modules/requirejs/bin/r.js:23452:47
```

_bundle.js needs to correctly sanitize the bundle variable name, to not include illegal characters, such as spaces.

in https://github.com/collective/generator-plonemockup/blob/91305ea844c0c777664378bcaf27478a5d87881e/app/templates/js/bundles/_bundle.js#L27

and

https://github.com/collective/generator-plonemockup/blob/91305ea844c0c777664378bcaf27478a5d87881e/app/templates/js/bundles/_bundle.js#L36

Start with app/templates/js/bundles/_bundle.js at the referenced lines and reproduce the failure using a project name containing spaces or other illegal characters. Done means the generated bundle variable name is valid JavaScript and Grunt completes without the esprima parse error.

Written by the indexing model from the issue text.