hide alert boxes after switching playlists

Fixes #42
show total time for lists.

Adds an observable that updates whenever list changes and corresponding
tmeplate bindings.
Medialist use 'self' instead of '_this'
Adds a delete button to playlist editor.

See #36 y #37. It needs a better look.
(cherry picked from commit 2c6a226a40a5d3eb38f74824c66a15a85a077771)
MediaListView: add a dummy row if list is empty (fixes #35)

Previously when the list was empty the table would not receive
any drop events.

We add one (only one) row so it works as expected.
(cherry picked from commit 394fbc0e0757e89e00604b8d09e9c9d38367bfe3)

Conflicts:

	public/js/views/medialist.js
Merge branch 'crear/merge/medialist-misc-try2' into airtime