The "Add Repository", "Add User", etc. buttons in the admin UI's change

list pages weren't very visible. They were just ordinary links in the

header.
This change converts them to a primary button presentation. This makes

them stand out clearly, helping users to notice them and know they can

be clicked to create a new entry for something.
The titles have also changed from "Add <object>" to "Add New <Object>",

with the "<Object>" being converted to title case (helping remove some

inconsistencies between different objects).

Went through the admin UI, looking at various model change list pages

and making sure they all looked as expected.