This is a complete design refresh for the extension UI. It makes use of

the config forms CSS components to provide a list of extensions that's

more in line with the look and feel of the integrations list, amongst

other bits of UI we're assembling, and presents information on the

extensions in a much clearer way than the old UI.
The new extension list presents each item as a row with three columns.

The first column contains all the extension metadata (summary, version,

author, description, load errors). The second column contains the status

(Enabled, Disabled, Error). The third column contains a vertical list of

actions that can be performed (Enable/Disable/Reload, Configure,

Database).
Above the list of extensions is a list of actions. This will always show

a "Reload Extensions" (replacement for "Scan for installed extensions").

If settings.DJBLETS_EXTENSIONS_BROWSE_URL is set, this will also

include a "More Extensions" button that navigates to that page. In the

process, the old template block for adding this sort of action has been

removed.
This new layout reduces the visual noise of the old layout, and makes it

easier to see and manage the states of all extensions.
The old template assumed it would be shown in the administration UI,

with standard Django administratino UI conventions. We still have a

template for that, but the meat of the new UI is in a reusable "parts"

template that can be embedded into any page.

Tested extensions in all possible states.
Tested the More Extensions and Reload Extensions buttons.
JavaScript and Python unit tests passed.