Handle disabled buttons

The "disabled" property of RightButtons was not handled.

android/app/src/main/java/com/reactnativenavigation/core/objects/Button.java

 package com.reactnativenavigation.core.objects;
 
 import android.content.Context;
-import android.graphics.Bitmap;
-import android.graphics.BitmapFactory;
-import android.graphics.drawable.BitmapDrawable;
 import android.graphics.drawable.Drawable;
-import android.net.Uri;
 import android.view.MenuItem;
 
 import com.facebook.react.bridge.ReadableMap;
-import com.reactnativenavigation.BuildConfig;
 import com.reactnativenavigation.utils.IconUtils;
-import com.reactnativenavigation.utils.ResourceDrawableIdHelper;
 
 import java.io.Serializable;
-import java.net.URL;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
     private static final String KEY_ID = "id";
     private static final String KEY_TITLE = "title";
     private static final String KEY_ICON = "icon";
+    private static final String KEY_DISABLED = "disabled";
 
     public String id;
     public String title;
     private String mIconSource;
+    public boolean disabled;
 
     private static final AtomicInteger sAtomicIdGenerator = new AtomicInteger();
     private static final Map<String, Integer> sStringToNumericId = new HashMap<>();
         id = getString(button, KEY_ID);
         title = getString(button, KEY_TITLE, "");
         mIconSource = getString(button, KEY_ICON);
+        disabled = getBoolean(button, KEY_DISABLED);
     }
 
     public boolean hasIcon() {

android/app/src/main/java/com/reactnativenavigation/core/objects/JsonObject.java

     }
     
     protected Boolean getBoolean(ReadableMap map, String key) {
-        return map.hasKey(key) ? map.getBoolean(key) : null;
+        return map.hasKey(key) && map.getBoolean(key);
     }
 }

android/app/src/main/java/com/reactnativenavigation/views/RnnToolBar.java

                     }
                     item.setIcon(icon);
                 }
+
+                if (button.disabled) {
+                    item.setEnabled(false);
+                }
             }
 
             RnnToolBar toolBar = mToolbarWR.get();