Make checkboxes look better in the General settings page

Summary:
Keep the checkbox text with the checkbox itself.
Fix the strange looking autosave option.

Test Plan: Logic.

Reviewers: Krita, ngraham, VDG

Reviewed By: ngraham, VDG

Subscribers: abetts, ngraham

Tags: Krita

Differential Revision: https://phabricator.kde.org/D15335