ANDROID: Modernize build system

Written originally by @Botje for ResidualVM

This code is essentially what we use for the ResidualVM Android build which will be available on the Play Store when 0.2.0 comes out.

The main issue with the build system is that it used deprecated tools, such as aapt, which are no longer present in the latest SDK versions. This updates the build process to use ant, which is supported by Google.

Currently though plugins are not built. Personally, I don't really see a need for plugins anymore as a full build is only 10mb and devices aren't particularly storage constrained these days. I can work on adding it back if there is interest in this approach.