Making cards look more like the originals

Moving custom styling from JS to CSS.
Introducing type-specific card type CSS classes for that (`card_type_text`, `card_type_image`, possibly in the future `card_type_html`).

The style has been adjusted to correspond to the demo cards shown in
the Glass Talk at SXSW. In particular, I have:

- Slightly reduced the Card height
- Used the Ultra Light font variant
- Adjusted the padding of the date stamp
- Added a slight text shadow
- Adjusted the text font style for image cards

Here's a screenshot for comparison, the bottom ones are cropped from the SXSW slides:
![Screen Shot 2013-04-05 at 6 15 12 PM](https://f.cloud.github.com/assets/811803/344914/989ce27e-9e0f-11e2-8ea2-ae072141f68b.png)

Feel free to ignore this pull request if you don't like the style updates ;-)