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

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

ortools/sat/samples/SolutionHintingSampleSat.java

@@ -14,6 +14,7 @@
 // [START program]
 package com.google.ortools.sat.samples;
 
+import com.google.ortools.Loader;
 import com.google.ortools.sat.CpModel;
 import com.google.ortools.sat.CpSolver;
 import com.google.ortools.sat.CpSolverSolutionCallback;
@@ -22,11 +23,8 @@ import com.google.ortools.sat.LinearExpr;
 
 /** Minimal CP-SAT example to showcase calling the solver. */
 public class SolutionHintingSampleSat {
-  static {
-    System.loadLibrary("jniortools");
-  }
-
   public static void main(String[] args) throws Exception {
+    Loader.loadNativeLibraries();
     // Create the model.
     // [START model]
     CpModel model = new CpModel();