Add MediaPlayer.setFlag JS API

It is used to set availability of playback actions.

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add playback control methods to MediaPlayer

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add MPRIS provider

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Don't add Nuvola to web app name

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>