Added new file upload preview

* Generic callback handler for uploads to allow different upload types
* Image preview when uploading an image
* Filename preview when uploading a non-image
* Cancel button added to upload
Removed two errant console.logs
Updated naming and added preview text

* Renamed clipboard to preview to better reflect actual
  feature
* Updated css/naming for said name changes
Changes per David Fowler

* Refactored duplicate code into single function call
* Removed dead code
* Renamed showClipboardUpload -> showUploadPreview
Minor refactoring

* Moved methods to general function area
* Removed UI method into a normal function
merged with index
Removed double quotes
Added comment and renamed variable

* Renamed $clipboardUpload to $previewUpload
* Added comment to non-obvious $uploadCallback
comment formatting
Merge pull request #892 from Buildstarted/dev

Added new file upload preview