Adding App Home to Slack app in Python.

Building on Creating a Slack App in Python on GCP, I wanted to continue extending reflect-slack-app to include an App Home.

The App Home screen allows each user in a workspace to have a personalized view powered by the app, which the app can use to share whatever data or interactions (buttons, etc) they want. Want to let folks configure their settings for your app? You can! Want to let folks see their most recent activity? You can! Want to let users know the current status on all open projects? You can!

The functionality is...