Issue #34 Use reprocess image instead of uploading

When an event is updated, if it the same url as before, do not attempt to create a
new image. Instead, use paperclip's image.reprocess! with new coordinate parameters.
Issue #31 Image load event handlers on render

Image loading event handlers should not be attached each time the image is loaded.
This results in duplicate event handlers.
Instead, attach special event handlers on render.
Issue #31 Don't check if url file exists add image
Issue #31 Clear image from model before save

When an image is being saved, be sure to remove all previous image properties first.
This is needed becuase if the image type switches, the old image might linger.
Merge branch 'master' of github.com:Forekasting/kiwi