Fix the size and pixel alignment of checkboxes and radiobuttons

Summary:
The checkboxes and radio buttons in plasmashell were signficantly different from checkboxes and radio buttons in the Breeze QStyle. This patch is needed to make D26271 look nicer.

• Plasmashell checkboxes and radio buttons were much larger.
  • 24x24 for checkboxes and 29x29 for radio buttons (Plasmashell) vs 16x16 (QStyle).
• Pixel alignment was very poor.
  • Checkbox indicator was 14x14, stretched to 24x24.
  • Radio button background was 22x22 or 32x32, adjusted to 29x29.
  • Radio button indicator was 16x16, stretched to 29x29.
• Style was different.
  • Checkbox indicators had sharper corners and less margin around the inner rectangle.
  • Radio buttons had a hardcoded dark gray circular frame and a shadow on the bottom of the inside of the frame.
  • Radio button indicators had less margin around the inner circle.

Test Plan:

Reviewers: Plasma, VDG, ngraham

Reviewed By: VDG, ngraham

Subscribers: ngraham, davidedmundson, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D26758