Bigger arrow on popover

[richardp-au]

I think popovers look better with bigger arrows (I'm currently using 12px and think it works well). This makes it more like iOS popovers which have a big arrow.

Tooltips should continue to have small arrows. This further differentiates tooltips and popovers where the former is more like a styled version of the built-in tooltips generally containing an alternative representation of the content or an explanation of the link/button, while the latter provides additional information and additional options (once again similar to iOS's popovers which can contain buttons/input).

[mdo]

I think they're fine as is, but thanks for the input :).