Aditional validation

* ```Virgilio.prototype.namespace$``` was able to create namespaces without name, so I added namespace name validator to check it. 
* Any Virgilio method or property could be changed with ```Virgilio.prototype.extend$```, including namespaces
Honestly, I think `\w` we can keep for now, dollar signs are used mostly for protected methods and not for namespace names, so this way we can nicely enforce that namespaces do not overwrite dollar-signed protected methods.