This helps to standardize the display of actions above a list through a

new djblets-c-config-forms-list-actions component. This is

intentionally very simple, just providing a basic set of classes to use

that can be styled or queried in a consistent way by a consuming

application. These are likely going to be mixed in with other classes

(such as djblets-l-config-forms-container for the list-actions and

something like btn for the djblets-c-config-forms-list-action).
The integrations list (currently the only part of Djblets using this

concept) has been updated to incorporate these classes.

Made sure the styles didn't impact anything on the Integrations page.
Tested this with an upcoming change to the Extensions page.