A few bugs in the preview crop image

1. Adding css (width, height and overflow) to the preview-pane
2. Closing preview-pane div (</div> missing)
3. Remove {% endthumbnail %}. For an unknown reason, the templatetag is not being recognized
4. The `#jcrop_preview_pane_{{ input_name }}` id should be #jcrop_preview_{{ input_name }} in lines 29 and 30
5. update_preview was not being called on JCrop(). onChange now calls update_preview instead of update_input. onSelect stills calls update_input
Merge pull request #4 from robertour/patch-2

A few bugs in the preview crop image