Fix issue with linking to a directory, add breadcrumb links

This PR is three-fold:

1. Fixes an issue where linking directly to a folder would yield a blank page (it would be passed through, since the `mime-type` was never `text`).
2. Adds links to individual breadcrumb elements
3. Adds a basic page for directories

The relation between the three points is obvious, with the ability to link to individual folders, there's actually some point to having the links in the breadcrumb. As a cool bonus, **the tree on the left reflects the active directory**, and will actually show the parent directories open by default. Neat!

A quick preview of the page:

![Selection_002](https://f.cloud.github.com/assets/382538/232841/90248086-8742-11e2-8440-ec5b4e2335dc.png)

**PS**: I did think about adding some sort of directory listing for the directory view, but ultimately decided against it, since it would simply be a repeat of what's on the tree.