Build module for all supported Android versions or let the user choose one (with a fallback)

The Android version for which the module is build is hardcoded to NOUGAT [(line 10)](https://github.com/Project-ARTist/module-sdk-gen/blob/88fde3e349428e3f21f51ab4a6836930b34d12bf/src/makefiles/core.mk#L10) in the core.mk file. It'd be better to support all versions or let the user choose it (with a fallback value).