Add documentation to Nuvola.MediaPlayer

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Move MediaPlayer public methods to top

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Finalize naming of JavaScript objects

  * Prototype objects are in UpperCamelCase, e.g. Nuvola.Core.

  * Instance objects are in lowerCamelCase, e.g. Nuvola.core.

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