Support livereload for `ionic cordova run browser`

origin: https://github.com/ionic-team/ionic-cli/issues/3036 and https://github.com/ionic-team/ionic-cli/issues/3036#issuecomment-376662587

We can inject all the Cordova www assets into the livereload dev server, providing a nice experience for developing mobile apps in `ionic serve`.

📝 Note: for developing cross-platform apps (attempting to target mobile AND desktop), I still highly recommend not using the Cordova browser platform. My reasoning is here: https://github.com/ionic-team/ionic-cli/issues/2312#issuecomment-365732607