Begins visual transfer or renderables from the previous item
to the new item.
function _initTransferableAnimations(item, prevItem, callback) {
        var callbackCount = 0;
        function waitForAll() {
            callbackCount--;
            if (callbackCount === 0) {
                callback();
            }
        }
        for (var sourceId in item.options.transfer.items) {
            if (_initTransferableAnimation.call(this, item, prevItem, sourceId, waitForAll)) {
                callbackCount++;
            }
        }
        if (!callbackCount) {
            callback();
        }
    }