[ticket/12506] Reposition post-buttons for compact layout

Fixes "Long post titles bump the username down an extra row beneath the edit/quote/delete buttons"

I added the `.has-profile` class to `post` because we use `.post` a lot, in very different contexts. Some are full (viewtopic), and some are very small/compact (post review/mcp/etc). This class will help us distinguish between "full" posts and "compact" ones.

![postbuttons-abspos](https://cloud.githubusercontent.com/assets/3015760/3614616/cd7d213e-0dc1-11e4-8f31-0b6549f070f6.png)

https://tracker.phpbb.com/browse/PHPBB3-12506
PHPBB3-12506
I actually don't like the look of moving the buttons further to the middle to make room for the "online" banner (as well as obviously taking up more space in responsive mode, which we don't want).

Not sure yet how to fix it. Perhaps reposition or change the online-styling in responsive mode.

As for the width, I'm not seeing any real problems. This would only be a problem if we had left/right borders. And even then we could probably use box-sizing.