Added size and position settings for initialization of image

Not sure if this is within the scope of what you want the plugin to do. But often when I use this, especially with dense SVGs, I want to focus on a certain part of the image, but still allow users to zoom out to understand the context of that cropped detail.

Also I like having the 'move' cursor enabled to give a hint as to the potential interactions available to the image without explicitly stating it. Let me know what you think or any code conventions you prefer since this is my first pull request.