android: Update to Qt 5.13
- Update android toolchain to current suggestions from Qt blog https://blog.qt.io/blog/2019/06/28/comply-upcoming-requirements-google-play/
This was only build-tested to the step were Qt is compiled. The motivation for upgrading Qt now is that we will get a much nicer file open dialog by default (for example in Kaidan) according to https://www.volkerkrause.eu/2019/02/16/qt-open-files-on-android.html
Edited by Jonah Brüchert