[ALOY-1042] Assets images not always correctly applied when using same theme for multiple platforms

For https://jira.appcelerator.org/browse/ALOY-1042
@feons Rather than explicitly setting themeChanged to true, should you update the build logger to make sure that buildLog.data.themeChanged is true? Otherwise, you're forcing assets to be recopied every time whether the theme has changed or not.