Ensure that the vertical spacing inside each panel is similar.
This makes the transition between each panel smoother and makes
the control center feel more cohesive.
Settings panels are given 32px above and below their content
and 32px vertical space between major sections. 12px space is
placed below headings.
Bluetooth, displays and printers are not addressed.
https://bugzilla.gnome.org/show_bug.cgi?id=786384
All the new panels have a standard 24px margin now, so
since we're already splitting the info pages into separate
panels, also fix this minor annoyance.
https://bugzilla.gnome.org/show_bug.cgi?id=779216