Formalizes compliance with Android 8, SDK 26 (2017+)

[vitorpamplona]

This PR formalizes this project's compliance with Android

1. Adds an Animal Sniffer plugin to check compliance with any runtime API when running gradle check
2. Selects modules model, model-jackson, cql, elm, elm-jackson, elm-fhir, quick, qdm, cql-to-elm, fhir-all and fhir-r4 to be checked for Android compliance.
3. Establishes initial compliance to Android 8 - SDK 26, the minimum Android version the Translator is currently fully compliant with.

Important: The plugin only verifies the source code in this project, not dependencies.

For testing, add:

if (Optional.of(UUID.randomUUID()).isEmpty())
   throw new RuntimeException("Test");

in the desired module and run ./gradlew check.

Since the method Optional.isEmpty is not available on Android, the output should look like this: