Bring back offsets for tooltips/popovers

As previously mentioned at https://github.com/twitter/bootstrap/pull/3081 there are some users who like to modify offset of their tooltips/popovers. Actually as @fat said in the linked pull request you could/should do that with CSS via `.tooltip.top { margin-top: -4px }` or `.popover.right { margin-left: -10px }` for example. But since v2.3.1 or something around then changing these values does not have any effect. So we either have to get rid off `.tooltip[.right|.left|.top|.bottom]` and `.popover[.right|.left|.top|.bottom]` or we gotta respect them in the calculation of our offsets.

Here you go. Maybe you'll use another solution but I wanted to push this issue forward... thanks