Set absolute path when uploadeding image

[Starefossen]

This PR allows you to set the absolute path when uploading an image. NB! This disables the random path. The final path to a version image follows the following rule: prefix + path + suffix + ext

var client = new Uploader('my-s3-bucket');

client.upload('/my/awsome/image.jpg', {
  path: 'custom/your/path/new_filename'
});

Signed-off-by: Hans Kristian Flaatten hans.kristian.flaatten@turistforeningen.no