UI: Repo header tweaks (#5945)

* UI: Repo header tweaks

- Use basic buttons on the header buttons, matching gogs
- Make 'Manage topic' text smaller, remove margin-left with no topics
present
- Move various inline styles to CSS
- Use flexbox on header title and buttons

* fix indentation

* reverse media query wrapping

* fix inconsisten whitespace

.editorconfig

@@ -15,7 +15,7 @@ indent_size = 8
 indent_style = tab
 indent_size = 4
 
-[*.{less}]
+[*.less]
 indent_style = space
 indent_size = 4