We should use KDE's Breeze style for our Windows builds in the future.

Advantages:

• Kleopatra looks the same on all platforms.
• The Breeze style is well supported for Windows because it's used for all Windows builds of apps published by KDE.
• We don't have to chase bugs in Qt's Windows styles (like T7414).

Disadvantages:

• We have to build and package the Breeze style.