reorganize all sat samples to have regular naming

Remove sub-method in C# sat sample, just use Main()

ortools/sat/samples/OptionalIntervalSampleSat.java

@@ -0,0 +1,37 @@
+// Copyright 2010-2018 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import com.google.ortools.sat.CpModel;
+import com.google.ortools.sat.IntVar;
+import com.google.ortools.sat.IntervalVar;
+import com.google.ortools.sat.Literal;
+
+public class OptionalIntervalSample {
+  static {
+    System.loadLibrary("jniortools");
+  }
+
+  public static void main(String[] args) throws Exception {
+    CpModel model = new CpModel();
+    int horizon = 100;
+    IntVar startVar = model.newIntVar(0, horizon, "start");
+    IntVar endVar = model.newIntVar(0, horizon, "end");
+    // Java code supports IntVar or integer constants in intervals.
+    int duration = 10;
+    Literal presence = model.newBoolVar("presence");
+    IntervalVar interval =
+        model.newOptionalIntervalVar(startVar, duration, endVar, presence, "interval");
+
+    System.out.println(interval);
+  }
+}