Reusable image uploading components, and use jQuery-File-Upload

* Create template upload_image.html for modal image upload panel
* Create reusable imageUploadPanel.js to control image upload panel
* Create utility function save_uploaded_image()
* Raise modal panel using Bootstrap markup, not JavaScript
* Use jQuery-File-Upload for ajax uploading (iframe on IE9)
* Eliminate redirect after upload, and its error-handling mechanism
Merge pull request #419 from RickMohr/reusable-image-uploading

Reusable image uploading components, and use jQuery-File-Upload