improve contact shadows support

- contact shadows are now supported for point and spot lights
- and are now independent from regular shadows, that is they can
  be enabled without enabling regular shadows

The only limitation currently is that the distance and step count for
ALL contact shadow are taken from the directional light options.

android/filament-android/src/main/cpp/LightManager.cpp

@@ -23,6 +23,13 @@
 using namespace filament;
 using namespace utils;
 
+extern "C" JNIEXPORT jint JNICALL
+Java_com_google_android_filament_LightManager_nGetComponentCount(JNIEnv*, jclass,
+        jlong nativeLightManager) {
+    LightManager *lm = (LightManager *) nativeLightManager;
+    return lm->getComponentCount();
+}
+
 extern "C" JNIEXPORT jboolean JNICALL
 Java_com_google_android_filament_LightManager_nHasComponent(JNIEnv*, jclass,
         jlong nativeLightManager, jint entity) {