Allow only images or all content from media feed

The changes here do not affect existing standalone functionality and defaults to the original behavior (only images are shown). This edit allows a user to turn off the images-only filter so other content types can be listed as well.

In-page usage can be dropped inline for custom or static pages like so:

<?php the_widget( 'null_instagram_widget', array(
                            'title' => 'Instagram',
                            'username' => $username,
                            'link' => 'Follow Us',
                            'wpiw',
                            'number' => 9,
                            'size' => 'thumbnail'),
                            'imagesOnly=0'
                        ); ?>