first version of parent directory header converted to buttons

Hi, i had an old feature added to dired to allow clicking on each part of a parent directory path with mouse1 to switch to that path. i added the same logic to neotree and removed the ".." link as duplicate of this new logic (debatable).

I'm pretty happy with it, but my testing has been light so far. One think I don't like is that I can't go "back" to the directory if i want to return after navigating to the parent, the same applied to the ".." link.

I was also thinking that it might be nice to be able to chroot with the mouse if I am walking the path to my target directory and don't want to switch to the keyboard to use C-c C-c. I couldn't find an easy way except splitting the + button from the dirname button but that seemed like too harsh of a change if you think people are used to the existing behavior.

Hope it works for you.

Cheers,
Rob

![image](https://cloud.githubusercontent.com/assets/129023/4346857/7bed0446-411b-11e4-8948-4020e94656db.png)