WIP deposit: new uploader component

* Adds Uploader - flight component for handling all different uploaders

* Adds PlUploader

* Adds DropboxUploader

Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>
CC @kneczaj @jmartinm: Please note this change in flightjs require path. Most other libraries depending on flightjs requires it with ``flight/lib/component`` instead of ``flight/component`` so this will make it easier to integrate other libraries.