implement sharing in iOS, add OpenGL renderer in OSX window

PanoPainter/GameViewController.m

@@ -70,6 +70,21 @@ std::recursive_mutex lock_mutex;
     [self.context presentRenderbuffer:GL_RENDERBUFFER];
 }
 
+- (void)share_file:(NSString *)file_path
+{
+    NSURL *url = [NSURL fileURLWithPath:file_path];
+    NSArray *objectsToShare = @[url];
+ 
+    UIActivityViewController *controller = [[UIActivityViewController alloc] initWithActivityItems:objectsToShare applicationActivities:nil];
+    
+    controller.excludedActivityTypes = @[];
+    controller.popoverPresentationController.sourceView = self.view;
+    controller.popoverPresentationController.sourceRect = CGRectMake(self.view.bounds.size.width/2, self.view.bounds.size.height/4, 0, 0);
+
+    // Present the controller
+    [self presentViewController:controller animated:YES completion:nil];
+}
+
 -(void)display_file:(std::string)filename
 {
     NSString* filePath = [NSString stringWithUTF8String:filename.c_str()];