Port Kvantum theme to QQC2

[UriHerrera]

The idea is to port the Kvantum themes to Qt Quick Controls 2. Design-wise the Kvantum theme can be used as a UI toolkit. I added text labels inside the SVG files here: https://github.com/nomad-desktop/nomad-kvantum-theme/tree/master/themes

Use Kvantum Managers' preview feature to see it in action.

Useful links:

• https://github.com/KDE/qqc2-desktop-style
• https://api.kde.org/frameworks/qqc2-desktop-style/html/index.html
• http://jriddell.org/2017/09/06/qqc2-desktop-style-beta-release/

[UriHerrera]

QQC2 theme is now being included a part of the framework.