Provide default leading nav button icon on iOS (#156)

* Add close icon image (ic_close_black_24px.png) to the iOS project asset catalog

* Fall back to iOS UIBarButtonItem.SystemItem.close for the leading nav button if no valid image path is provided

* Bump version number

Author: JamieDass

example/ios/example/Images.xcassets/AppIcon.appiconset/Contents.json

@@ -2,37 +2,52 @@
   "images" : [
     {
       "idiom" : "iphone",
-      "size" : "29x29",
-      "scale" : "2x"
+      "scale" : "2x",
+      "size" : "20x20"
     },
     {
       "idiom" : "iphone",
-      "size" : "29x29",
-      "scale" : "3x"
+      "scale" : "3x",
+      "size" : "20x20"
     },
     {
       "idiom" : "iphone",
-      "size" : "40x40",
-      "scale" : "2x"
+      "scale" : "2x",
+      "size" : "29x29"
     },
     {
       "idiom" : "iphone",
-      "size" : "40x40",
-      "scale" : "3x"
+      "scale" : "3x",
+      "size" : "29x29"
     },
     {
       "idiom" : "iphone",
-      "size" : "60x60",
-      "scale" : "2x"
+      "scale" : "2x",
+      "size" : "40x40"
     },
     {
       "idiom" : "iphone",
-      "size" : "60x60",
-      "scale" : "3x"
+      "scale" : "3x",
+      "size" : "40x40"
+    },
+    {
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "size" : "60x60"
+    },
+    {
+      "idiom" : "iphone",
+      "scale" : "3x",
+      "size" : "60x60"
+    },
+    {
+      "idiom" : "ios-marketing",
+      "scale" : "1x",
+      "size" : "1024x1024"
     }
   ],
   "info" : {
-    "version" : 1,
-    "author" : "xcode"
+    "author" : "xcode",
+    "version" : 1
   }
-}
+}

example/ios/example/Images.xcassets/Contents.json

@@ -1,6 +1,6 @@
 {
   "info" : {
-    "version" : 1,
-    "author" : "xcode"
+    "author" : "xcode",
+    "version" : 1
   }
 }

example/ios/example/Images.xcassets/ic_close_black_24px.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "ic_close_black_24px.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "ic_close_black_24px@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "ic_close_black_24px@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

example/ios/example/Images.xcassets/ic_close_black_24px.imageset/ic_close_black_24px.png

@@ -215,10 +215,15 @@ - (void)loadDocumentViewController
 
     if (self.showNavButton) {
         UIImage *navImage = [UIImage imageNamed:self.navButtonPath];
-        UIBarButtonItem *navButton = [[UIBarButtonItem alloc] initWithImage:navImage
-                                                                      style:UIBarButtonItemStylePlain
-                                                                     target:self
-                                                                     action:@selector(navButtonClicked)];
+        UIBarButtonItem *navButton;
+        if (navImage == nil) {
+            navButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(navButtonClicked)];
+        }else{
+            navButton = [[UIBarButtonItem alloc] initWithImage:navImage
+                                                         style:UIBarButtonItemStylePlain
+                                                        target:self
+                                                        action:@selector(navButtonClicked)];
+        }
         self.documentViewController.navigationItem.leftBarButtonItem = navButton;
     }
 

example/ios/example/Images.xcassets/ic_close_black_24px.imageset/ic_close_black_24px@2x.png

@@ -1,7 +1,7 @@
 {
   "name": "react-native-pdftron",
   "title": "React Native Pdftron",
-  "version": "2.0.1-beta.20",
+  "version": "2.0.1-beta.21",
   "description": "React Native Pdftron",
   "main": "index.js",
   "scripts": {