Fixes #130, make CFBundleIdentifier dependent on package name if not set...

Make CFBundleIdentifier dependent on package name if not set in options. Fixes issue #130.

CFBundleIdentifier will look like this `com.node-webkit-builder.[packagename]` where `packagename` is the lowercase, striped of `[^a-z\-]` version of `CFBundleName` ([see Apples guidelines](https://developer.apple.com/library/mac/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html)).