Implement config editor

[dglazkov]

To use our cool new config system, let's make editing configs easy.

The pattern I want to try is this:

• Config system provides two Flask routes: one for GET and one for POST.
• The GET route renders Web UI for editing configuration and uses POST route to update the the config
• The route takes *ConfigStore and *Config type as a parameter
• When I need to edit config, I start a Flask server, add these routes to it
• ✨