Fix zip.workerScriptsPath backward compatibility issue and deprecate zip...

Fix zip.workerScriptsPath backward compatibility issue and deprecate zip workerScriptsPath.
> I just want to avoid unnecessarily breaking applications when users upgrade zip.js. 

In which case applications can break if we don't allow using workerScriptsPath and workerScripts together?

>Supporting concatenation comes at no cost

Not true if we feel the concatenation behavior is not ideal in future - for backward compatibility we can never change it. In contrast, if we don't support it now, we still have the chance to add it in future according to users' feedback.

In your use case, can this work? 
```obj.zip.workerScripts = [ app.baseURL + 'zipjs-worker.min.js' ]```
I'm not sure what does "set elsewhere by a build to" mean.