Use Media.Piece in Playlist , fixes #49

When adding a new Media to a List we instance a Piece with a 'checksum'
field pointing to the Media's md5.

Also we set up the correct urls for Piece and Block.
start: use make

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>
add basic travis file

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>
Merge pull request #95 from inaes-tic/xaiki/travis

make travis STFU. yes thank you!
Merge remote-tracking branch 'remotes/origin/crear/pieces-2'
Discard change in url/urlroot for media.piece and media.block.
Modify url/urlroot in schedule for consistency with other models