Implement support for Android Studio.

This change incorporates all the necessary build files, packaging changes, makefile
tweaks and documentation needed to make openFrameworks work on Android Studio.

This resolves issue #3408.
I agree, actually. However, if the file is in `libs/openFrameworksCompiled/projects/android` then the project cannot be imported into Android Studio without first moving the file back out again.

I actually originally had it in `libs/openFrameworksCompiled/projects/android`, and had it hoisted out to the root by the `create_package.sh` script. But this makes it harder for people downloading the package via `git` to use it directly.

If you're OK with that, I'll move it back.