Android: add variables for APP_NAME, APP_PACKAGE, EXECUTION_TARGET

Developing APPs for Google for Work | Android - managed Devices APKs must be built for different Environments with different Package Name.
Same happens also for normal Devices if APP should be tested against different backends or so.

see this blogpost where a workaround is described HowTo change some things to get this run: https://gympulsr.com/blog/qt/2017/03/02/multiple-versions-with-qt.html

Would be much easier and more intuitive if it was possible to set these variables inside .pro and the rest is done by Qt build process.

see some more infos: https://appbus.wordpress.com/2017/03/15/overview-managed-android-devices/