Prepare for Heroku deprecation: Migrate to self-hosted config panel

[unlobito]

skunk's latest release (v1.6.0, from 2016-08-23!) relies on Heroku to host https://github.com/unlobito/skunk-config for the config panel and barcode bitmap rendering. This won't be sustainable beyond 2022-11-28 due to changes in Heroku's free dyno offering (#34 / Heroku's Next Chapter).

⚠️ skunk-config.canidae.systems isn't ready for public use. This PR and https://github.com/unlobito/skunk-config/pull/7 will be merged once the dust settles.

• [x] package.json: maintenance version bump (v1.6.1)
• [x] README.md: link to Rebble App Store
• [x] pebble-js-app.js: use self-hosted config panel
• [x] publish new build

[unlobito]

turns out-

Version label for the app. Must use the format major.minor.0. (https://developer.rebble.io/developer.pebble.com/guides/tools-and-resources/app-metadata/index.html)

resolved in b855a2a. this PR's build artefacts should now permit access to skunk-config via skunk-config.canidae.systems. will merge after testing.