Use eslint-plugin-import-order-alphabetical in place of import/order rule

[randycoulman]

In #117, we enabled some support for sorting of import statements, but couldn't get all the way to where we want to be (see discussion in #103).

The PR on eslint-plugin-import is still open. Occasionally, someone will pick it up and try to run with it, but it's still out there.

Per this comment, there is now a new plugin available, eslint-plugin-import-order-alphabetical that contains an auto-fixing version of this open PR.

We've experimented with that plugin on a client project and found it to work quite well. It still doesn't support the names within a single destructured import statement, but it does get us a step closer.

Suggested rule configuration to match our conventions:

    "import-order-alphabetical/order": [
      "warn",
      {
        groups: [
          ["builtin", "external"],
          "internal",
          "parent",
          ["sibling", "index"],
        ],
        "newlines-between": "always",
      },
    ],