New port: x11-toolkits/qt5-charts

Qt released some fancy classes to draw nice charts:
https://blog.qt.io/blog/2016/01/18/qt-charts-2-1-0-release/

With Qt 5.7 this will come bundled as a submodule.
For now we can fetch it from github.

This is based on the version by Marie Loise Nolden from
our experimental Qt-5.7.1 ports.

Submitted by: Marie Loise Nolden <nolden@kde.org>
Reviewed by: rakuco
Approved by: rakuco (mentor)
Differential Revision: https://reviews.freebsd.org/D8648