Moved from https://github.com/backdrop/backdrop-issues/issues/1399#issuecomment-204...

As per @jenlampton's comment, this might be too hasty to implement in 1.x and should be better of for 2.x. Not setting the milestone right away. Waiting for more input.

...final step: move the admin pages for modules, themes and layouts as primary tabs of the same "Extend Backdrop" page:

backdrop-pb-manage_modules_themes_and_layouts_as_primary_tabs

GitHub Link: 
https://github.com/backdrop/backdrop-issues/issues/1780
GitHub Issue #: 
1780