D18215: Improve the preferences-desktop-cryptography icon

[TrickyRicky]

trickyricky26 added a reviewer: VDG.

REPOSITORY
  R266 Breeze Icons

REVISION DETAIL
  https://phabricator.kde.org/D18215

To: trickyricky26, #vdg
Cc: kde-frameworks-devel, michaelh, ngraham, bruns