update to dash 1.0, plus R build

[alexcjohnson]

closes #29
Updates tests here to use dash.testing, and more standardized build commands.

Adding R support turned out to be a lot simpler than #72 made it look - basically, adding in r_prefix and using it in the dash-generate-components call means it all just works ™️ - I added some tests that the right files (R and otherwise) are present after building.

This is ready for review, but should not be merged until plotly/dash#801 is merged and released so we can point to a released version of dash in the various requirements.txt files.

[bcliang]

Please consider updating package.json with upgraded devDependency eslint to 5.16.0. The main thing here is that it closes a vulnerability in [email protected]

  "devDependencies": {
...
    "eslint": "^5.16.0",
...
  },

[alexcjohnson]

Please consider updating package.json with upgraded devDependency eslint to 5.16.0

Now eslint is up to v6. Updated all of package.json, and the necessary dash changes have been released so we use that as well. @byronz ready for review.

[byronz]

no need to have pytest relevant dependencies here as dash[testing] will control that

[byronz]

same here: percy adn selenium will be installed by dash[testing]

[alexcjohnson]

For that matter I don't know why we need anything other than dash[testing]... none of our other repos require chromedriver-binary, and I don't see ipdb, flake8, or pylint used - do you see any reason we should keep those?

[byronz]

if not needed, I'm fine to 🔪

[byronz]

💃