rename Build fields: version -> versionName, vercode -> versionCode

rename Build fields: version -> versionName, vercode -> versionCode

Since the YAML/JSON/etc. field names are now exactly the same as the field
names used in the internal dict in the Build class, this is a global rename

This keeps with the standard names used in Android:
https://developer.android.com/guide/topics/manifest/manifest-element.html