Adapt to new plugin mechanism

[k-toumura]

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

Proposed changes

• adapt to new plugin mechanism(node-red/designs#39) to enable linter function in Node-RED Editor.
• eliminate complicated WebPack dependency to focusing on core functionality. Plugin nrlint-plugin-func-style-eslint is able to used only on CLI.
• Because Node-RED plugin implementation(node-red/node-red#2779) is work-in-progress, this PR doesn't fully work. For example, configuration of linting rule can't be read from $NRHOME/settings.json, but it is hardcoded in nrlint.html.

Checklist

• [x] I have read the contribution guidelines
• [ ] For non-bugfix PRs, I have discussed this change on the forum/slack team.

[knolleary]

I'm going to merge this as-is rather than try to review this changes on top of the base code that I haven't properly review yet.