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

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

ortools/linear_solver/samples/SimpleMipProgram.java

@@ -15,6 +15,7 @@
 // [START program]
 package com.google.ortools.linearsolver.samples;
 // [START import]
+import com.google.ortools.Loader;
 import com.google.ortools.linearsolver.MPConstraint;
 import com.google.ortools.linearsolver.MPObjective;
 import com.google.ortools.linearsolver.MPSolver;
@@ -23,11 +24,8 @@ import com.google.ortools.linearsolver.MPVariable;
 
 /** Minimal Mixed Integer Programming example to showcase calling the solver. */
 public class SimpleMipProgram {
-  static {
-    System.loadLibrary("jniortools");
-  }
-
   public static void main(String[] args) throws Exception {
+    Loader.loadNativeLibraries();
     // [START solver]
     // Create the linear solver with the SCIP backend.
     MPSolver solver = MPSolver.createSolver("SCIP");