Made domain name a settable domain name option

[crisner]

Fixes #306 (<=== Add issue number here)

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• PR is descriptively titled 📑 and links the original issue above 🔗
• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
• code is in uniquely-named feature branch and has no merge conflicts 📁
• screenshots/GIFs are attached 📎 in case of UI updation
• ask @publiclab/reviewers for help, in a comment below

We're happy to help you get this ready -- don't be afraid to ask for help, and don't be discouraged if your tests fail at first!

If tests do fail, click on the red X to learn why by reading the logs.

Please be sure you've reviewed our contribution guidelines at https://publiclab.org/contributing-to-public-lab-software

Thanks!

[crisner]

The domain name can be passed as a settable option through the embed control as:

L.control.embed({
   hostname: 'hostname'
});

and also passed as an option in LEL as:

L.LayerGroup.EnvironmentalLayers({
        baseLayers: {
          'Grey-scale': baselayer1
        },
        hash: true,
        embed: true,
        hostname: 'hostname'
      }).addTo(map);

Screenshot defaulting to Public Lab's gh-pages:

Screenshot after adding a domain name:

[crisner]

Changes made in this PR include formatting the edited layers and adding a new rule to the eslint config file.

[sagarpreet-chadha]

Awesome!