add istanbul to requirements

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
separate mocha arguments

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
add coverage target

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
put back some of the playlists tests

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
set coverage as the default test script for travis

Signed-off-by: Tomas Neme <lacrymology@gmail.com>