local-webserver plugin lets android builds fail

I use the WKWebViewEngine plugin together with local-webserver (due to CORS restrictions when trying to load e.g. local audio files to play back using WebAudio). However, the local-webserver plugin modifies the `<content>` tag in my config.xml, affecting all platforms, and making android builds not work anymore. This is quite bad and in my opinion a plugin should never touch the config.xml file but only provide settings etc. via the regular plugin mechanism.

My workaround is to override the content value inside a `<platform name="android">` block of my config.xml. And this is what the local-webserver plugin should do. It should just put the content override in the iOS platform tag, and not use hook scripts.