R1:bb369c7b711f

Convert the "Repository Management" UI to a full-width, Phortune-style UI

Summary:
Ref T13216. I want to add some new management options to repositories (e.g., filesize limit, clone timeouts). Before adding new stuff here, update the UI to a full-width, Phortune-style UI.

This partially reverts D18523. About a year ago, several UIs got converted to fixed-width (repository management, config, settings, instance management in SAAS). I didn't think these were good changes and have never really gotten used…