Fixing several issues in datasets item

- [x] Description should support markdown
- [x] Dataset secondary info should be bigger
![screen shot 2014-12-26 at 15 33 52](https://cloud.githubusercontent.com/assets/132146/5557969/af13e8ea-8d14-11e4-98d9-7c3db3042575.png)
- [x] Dataset size should have only one decimal.
- [x] Link and password protected datasets doesn't have any color.
- [x] Item icon when dataset is a raster doesn't appear