throw an exception if an app is missing jars and a WAR is being built

[andy-berry-dev]

We currently log a warning if an app has a WEB-INF directory and is missing brjs-* jars from libs/java/application - something like The app 'it-app' is either missing BRJS jar(s), contains BRJS jar(s) it shouldn't or the BRJS jar(s) are outdated. You should delete all jars prefixed with 'brjs-' in the WEB-INF/lib directory and copy in all jars contained in sdk/libs/java/application..

This is OK for a general warning when using the dev server but the warning gets lost in various other logs when building a war. This means it's very easy (both @thecapdan and I did it) to not see the message, build a WAR and then wonder why it doesn't work in prod - eventually finding in the logs that you're missing loads of classes.

If we're running brjs build-app -w we should throw an exception if there are missing/different brjs-* jars and continue with the existing warning log for any other commands.

This should be reasonably trivial to fix so I'd suggest it's done ASAP since it's an easy bug to come across. // @dchambers