The old integrations UI worked alright when we only had a few

integrations available, but didn't scale well. It was harder to visually

separate the configurations from the available integrations, and really

hard to see at a glance how many configurations you had in total. It

also only worked in the Django administration UI, meaning it wasn't

usable in, say, RBCommons or Splat Team Admin UIs.
This change completely redoes the UI for integrations, while at the same

time making it suitable for use outside of the Django administration UI.

Now, configurations are presented as a config forms list, showing an

icon for the integration, the configuration name, integration name, and

the enabled/disabled state.
Above the list is a button for adding an integration, which pops up a

tile-based menu of all integration options. Down the road, this can be

expanded to allow searching or filtering based on categories, but for

now it provides a good way of quickly seeing what's available.
The new UI has been built on top of the new config forms work, providing

a consistent appearance wherever it's embedded.

Tested adding new integrations via the popup.
Tested editing existing integrations.
Tested the integrations popup on various screen sizes, including very

large and very small screens.
Tested that the integration state was reflected in the list item.
Tested custom URL namespaces, and that they're respected everywhere.