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 mvn test
2. Selects modules engine, engine.fhir and engine.jackson 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 mvn animal-sniffer:check.

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

[JPercival]

Is there a version of this plugin that hooks into the compiler so that devs get immediate feedback prior to a build? Something like ErrorProne?

<plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.8.0</version>
        <configuration>
          <source>8</source>
          <target>8</target>
          <encoding>UTF-8</encoding>
          <compilerArgs>
            <arg>-XDcompilePolicy=simple</arg>
            <arg>-Xplugin:ErrorProne</arg>
          </compilerArgs>
          <annotationProcessorPaths>
            <path>
              <groupId>com.google.errorprone</groupId>
              <artifactId>error_prone_core</artifactId>
              <version>${error-prone.version}</version>
            </path>
          </annotationProcessorPaths>
        </configuration>
      </plugin>