UK: media_add_uri - add to xform uri media resource
UK: ensure url media links have a hash and are valid urls
UK: add media url html form
UK: when deleting a media file ensure filename is not an empty string
UK: test add media url, closes #280
UK: if statements merged with or
UK: code refactor: add create_media function, use constants for chunk_size and whence
UK: file should exist and not be empty string
UK: specify when to download a media url
UK: pep8
UK: for the case where the file does not exist and it is not a media url
Merge pull request #283 from onaio/280-link-as-media

link as media