MediaListView: adds 'type' attribute.

type is a combination of:

  - sortable (like the current playlist on Edit Playlists)
    has full drag and drop, can edit name and remove elements
  - draggable (like the left pane on Edit Playlists)
    cannot edit name nor remove elemens, dragging is enabled
  - searchable (like the one on Browse Medias)

Plus 'fixed' and 'readonly' modifiers.

The one that grants most permissions wins ( sortable > draggable > searchable ).
But, 'readonly' beats all.

'fixed' disables the 'x' at the top rigth to close a list.
Merge branch 'crear/merge/playlist-type' into airtime
Closes pull request #66
Modified views/templated/medialist.jade to use _id field instead of checksum

Signed-off-by: Diego Gaustein <diego@gaustein.com.ar>

Conflicts:
	views/templates/medialist.jade