add support for alpha of all scrollbar and radius configuration

example of the custom configuration: 

    BRScrollBarController *brScrollbarSchool = [BRScrollBarController initForScrollView:self.tableView onPosition:kIntBRScrollBarPositionRight delegate:nil];
    brScrollbarSchool.scrollBar.backgroundColor = [UIColor greenColor];
    brScrollbarSchool.scrollBar.hideScrollBar = NO;
    brScrollbarSchool.scrollBar.cornerRadius = 0;
    brScrollbarSchool.scrollBar.originAlpha = 1;
    brScrollbarSchool.scrollBar.scrollHandle.backgroundColor = [UIColor blackColor];
    brScrollbarSchool.scrollBar.scrollHandle.alpha = 1;
    brScrollbarSchool.scrollBar.scrollHandle.cornerRadius = 3;