make(java): Migrate samples to maven (#202)

- Factorise makefile code using advanced make function
- Use the Loader in samples

ortools/constraint_solver/samples/SimpleRoutingProgram.java

@@ -16,6 +16,7 @@ package com.google.ortools.constraintsolver.samples;
 // [START import]
 import static java.lang.Math.abs;
 
+import com.google.ortools.Loader;
 import com.google.ortools.constraintsolver.Assignment;
 import com.google.ortools.constraintsolver.FirstSolutionStrategy;
 import com.google.ortools.constraintsolver.RoutingIndexManager;
@@ -27,13 +28,10 @@ import java.util.logging.Logger;
 
 /** Minimal Routing example to showcase calling the solver.*/
 public class SimpleRoutingProgram {
-  static {
-    System.loadLibrary("jniortools");
-  }
-
   private static final Logger logger = Logger.getLogger(SimpleRoutingProgram.class.getName());
 
   public static void main(String[] args) throws Exception {
+    Loader.loadNativeLibraries();
     // Instantiate the data problem.
     // [START data]
     final int numLocation = 5;