More forgiving image height/width requirements

[brockfanning]

Currently the image for the image map is required to have "height" and "width" attributes in the HTML markup. Otherwise, a javascript alert pops up. This update does 2 things:

1. Use a console log instead of an alert. The reason for this is that this library may be used in CMS situations, potentionally with AJAX edit-in-place functionality, and a javascript alert can cause issues when a user tries to save their work but forgot to include height/width.
2. Try to get the dimensions of the image through javascript, before giving up. This is useful if Mapify is to be implemented on a site that already has existing image maps throughout it, many of which may not have height/width attributes on the image.