For Travis CI - skip APK test run when packaging.
General build script cleanup:
- Constrain build option values in cmake-gui.
- Constrain build configuration for both multi-configuration and single-configuration generators.
- Mark cached variables as advanced or internal as appropriate.
Enhance Rakefile to autoload other *.rake scripts in ".rake" directory.
Also create symlink to Rakefile when scaffolding.
[ci skip]
Merge branch 'cleaning-up-build-scripts-for-android' into master.
For Travis CI - switch CI build to use Android build environment.