[feature] Prototype a Heroku deployment of hosted cellxgene (#1427)

* hello world

* stuff

* successful build

* updates"

* maybe a basic example

* simplify

* reamde into dockerfile

* some more stuff

* Release procfile

* package.json at top levle

* don't release in procfile for now

* more package.json stuff

* copy assets

* merge master

* not in the relase phase

* revert not necessary

* pin gunicorn version

* reset common.mk

* Update package.json

Co-authored-by: Madison Dunitz <dunitzm@gmail.com>

package.json

@@ -0,0 +1,6 @@
+{
+  "name": "cellxgene",
+  "scripts": {
+    "postinstall": "npm install --prefix client && npm run build --prefix client && make copy-client-assets"
+  }
+}