Add debug mode start scripts

[bartbutenaers]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Docker allows us to setup very easy new (test) environments. However it would be nice if we could connect with a debugger to a Node-RED instance, to have remote debugging capabilities.

This pull request only adds two new scripts ('debug' and 'debug_brk') to the package.json file(s), to accomplish this.

I have discussed this new feature in this Discourse discussion, where I got a green light from @dceejay :-)

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality