Rework the error messages on different platforms in different situations

Affecting factors:

- requested platforms
- platforms added to the project
- installed SDKs
- if platform is available on system at all (e.g. iOS is not available on linux)
- if it is build or run (should the errors be ignored or not?)
Only add platform to the cordova project if it has the SDK installed
Don't try to hack into AndroidManifest if Android is not requested
Skip the whole build if there is nothing to build for
Don't copy the builds of platforms we didn't build for