Add `console.log` with hint to use `--prod` for non-prod builds

[jgw96]

From @janpio on July 20, 2017 8:17

I'm submitting a ...
[ ] bug report
[x] feature request

Current behavior:
Many new users don't know they should be using --prod to get an app with a faster startup time.

Expected behavior:
A console.log output for non-prod builds that says something like "Add --prod to your build command for faster app boot time" on startup could help to point them into the right direction.

Copied from original issue: ionic-team/ionic-framework#12417

[jgw96]

Hey @janpio , I think this is a great idea. As this would be something that would have to be implemented in app-scripts and not the framework, im gonna move it over to app-scripts.