Setup travis build to run tests on the Android emulator

[rhardih]

Initially https://github.com/benlau/qtci looks like the way to go.

Todo

• Create travis config which installs, as minimum, Qt 5.12. See https://github.com/benlau/qtci/blob/master/.travis.yml for reference.
• Modify travis config to build tests project with installed version of Qt.
• Add install of Android emulator to travis config. This blog post might be of inspiration.
• Deploy and run built version of tests project on installed emulator and extract exit code to build status.