Smarter way to set Cordova platform version number

I find it really unfortunate that we have to use tooling to set Cordova platform versions in multiple places such as package.json, generated cordova.js, VERSION file, Android Gradle file, etc.

I think it should be relatively straightforward to update the Cordova tooling so that we can mark the version in package.json and the scripts would generate the platform files with the correct version where it is needed whenever the user does `cordova platform add`.

And I suspect that in Gradle we should be able to define a constant or variable with the version in one place and reference it in the other places.