fix default value of sound notification, fix player for mentions

current default value is outside the range [0, 1], here is quick fix.

to play DM sound notification just type in browser console (on pages with **player** object such as _home.html_ or _options.html_):

    $.MAL.soundNotifyDM();

to check current value:

    $.Options.getOption('playerVol',1);

to check kind of sound (response must be positive to playing):

    $.Options.getOption('sndDM', "false");