Noborder style

Hello guys,
Thank you for the work you have done with this small project.
I needed  a new border style, a more simple one just like the one in the screenshot.
It has no corner radius and the content view controller's view extends on the popover full size.

I added a new tint: FPPopoverNoBorder. When using it you also would probably want to set the background color that will also fill the arrow, so i added a new property in the FPPopover view contentBackgroundColor.

![Screen 20Shot 202013-02-07 20at 2010 22 49 20PM](https://f.cloud.github.com/assets/189993/137184/2446bafc-7165-11e2-804e-306e8e14fd37.png)