Crear/merge/playlist type

This depends on #65 
There's discussion about this issue at https://github.com/inaes-tic/mbc-playout/commit/e080b8e37fe229f0a94c8264964fe0fd1b5b24e1 and https://github.com/inaes-tic/mbc-playout/commit/9f4696eb9d650c34806eab5a8869e8a029d10386

 Adds a 'type' attribute to MediaListView
    
 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.