Packaged teslamate

- Need to provide RELEASE_COOKIE environment variable when running the
  app (https://github.com/NixOS/nixpkgs/issues/166229)

- Deploy script has an output directory hardcoded that doesn't play nice
  with nix. I made change and generated a patch file with `git diff` in
  my local copy of the repo. I also had to make sure to change the
  filepaths in the patchfile to remove the `assets/` prefix. The
  contents of the this directory must be moved to `priv/static/assets`.

- Have to manually install the phoenix node dependencies (these aren't
  fetched from npm, but from the repo itself).

packages/teslamate/deploy_output.patch

@@ -0,0 +1,13 @@
+diff --git a/scripts/build.js b/scripts/build.js
+index 86a42678..569702b1 100644
+--- a/scripts/build.js
++++ b/scripts/build.js
+@@ -4,7 +4,7 @@ const { sassPlugin } = require("esbuild-sass-plugin");
+ const esbuild = require("esbuild");
+ 
+ const ENTRY_FILE = "app.js";
+-const OUTPUT_DIR = path.resolve(__dirname, "../../priv/static/assets");
++const OUTPUT_DIR = path.resolve(__dirname, "deploy_output");
+ const OUTPUT_FILE = "app.js";
+ const MODE = process.env["NODE_ENV"] || "production";
+ const TARGET = "es2017";