added a FPPopoverCustomTint

Hello,
I added the feature to specify the colors for the popover in the form of

    CGFloat colors[4];
    colors[0] = 0.18; colors[1] = 0.30; colors[2] = 0.03; colors[3] = 1.0;
    //// your base color
    CGFloat gradientColors[8];
    //// your gradient
    popover.customColors = colors;
    popover.customGradientColors = gradientColors;

Maybe it is something might interest you.

regards,
Marco