adding circle icon for slider handle. fixes #552
Revert "adding circle icon for slider handle. fixes #552"

This reverts commit aea19f007abcb086e5a5055c44011f368a267296.
Merge remote-tracking branch 'upstream/master'
Several minor code improvements.
Actually, tracks.js contains several pieces of code which could
be re-written more effectively. The problem is that in some places
there are conditional checks like this:

    if (condition) {
        call_setter( true);
    } else {
        call_setter( false);
    }

which could be re-written to:

    call_setter( condition);

This improvement saves some bytes of code length, traffic and should
also work more effectively by utilizing less machine resources
Code guidelines fixed
Merge pull request #576 from Mikhus/master

Some minor code improvements
export Component.prototype.fadeIn/Out
Merge branch 'default-volume' into onion-prod