refs #34: updated the tests for expected behaviour for base 64 encoding of image data.
refs #34: store and pass around the image data, instead of the image path
refs #34: image handler now deals with image data and base 64 encodes it instead.
refs #34: since we no longer write the image to disk, we no longer need to copy the file to a temp dir.
refs #34: passed along the filename, correctly created the src for image (using the correct file extension)
Merge pull request #34 from OpenScienceFramework/issue_34

Make the default image handler a bit more useful