Duplicate padding in CupertinoFormSection usage on Settings page

[navaronbracke]

The CupertinoFormSection widget has a bug where its padding is added twice.

The app adjusts some padding values according to this double padding in the Settings page.
Once the fix has landed in stable, we should remove the double padding.

TODO:

• the excludedTermsListFooter on iOS should only use 20 horizontal padding (there is an existing comment explaining the bug)
• review the layout of other iOS widgets on the Settings page. With the fix for the padding, the layout might have shifted a bit.