UI redesign/immediate goals

[timkpaine]

This is an area to discuss the UI redesign, including the port to mui/react.

My immediate non-UI goals are to tighten up the storage, authentication, and scheduler backends. The following are the immediate issues:

• there is too much SqlAlchemy specific code. I will be adding a mongodb backend (Backends #58) so I can identify shared patterns
  -the airflow code is brittle and requires a local airflow instance. I have the skeleton of a remote airflow worker, so i'm going to setup an airflow instance in the cloud to test. I am also going to add support for luigi (Add Luigi backend #57) to identify shared patterns as above
• the authentication code is too SqlAlchemy specific. I'm going to add support for authenticating through the airflow instance, and via something like oauth

While this is going on, I think it makes sense to identify what this product should look like, and to just generally go through some UX flow mockups.

CC @blink1073 @eriknw