fix : import-picture-panel

- When imported 1 picture and then importing another one, the picture
  preview was not cleaned and was displaying the two images side by side.
  Fixed in ImportController.js
- Switched all double-quoted strings in ImportController to single-quoted
  strings. Should enforce this using jshint
- Aligned all inputs in the import picture panel
- Renamed 'Preview :' import section to 'Info :'. Mostly it's to make it
  shorter, but also I'd like to display additional information to the
  right of the preview in the future.