The new widget displays 8 repositories (rather than 3) in a grid. Each

entry contains the name of the repository, the service (SCMTool type and

hosting service), and action links for viewing the other repositories or

adding a new one.
If there are no repositories configured, helpful instructions are added

for configuring a new one, along with a link to the manual.
This new implementation is based on top of the new BaseAdminWidget

class, moving away from the old Widget. It also uses CSS Grid to lay

out the repositories. While we haven't opted to use this elsewhere in

the UI, this is safe for this limited case.

Tested with and without repositories, and in desktop and mobile modes.