Add markdown support for descriptions

### Test case description

## Collapsed
![2014-12-11 17 35 36](https://cloud.githubusercontent.com/assets/2149631/5395641/30ec53bc-815c-11e4-895b-665462d0a97e.png)

## Expanded
![2014-12-11 17 38 55](https://cloud.githubusercontent.com/assets/2149631/5395697/afc257c2-815c-11e4-88ec-e2396b7b92ff.png)

## Test suite description
![2014-12-11 17 35 44](https://cloud.githubusercontent.com/assets/2149631/5395646/3b0c5464-815c-11e4-8a82-ea81b540d60a.png)


@lanwen compare
when use '=': `ng-show="testcase.description.value"`
when use '@' `escape-html="{{testcase.description.type != 'markdown'}}"`
it means that = goes to scope to get value, but @ gets attribute value. it allow you to use `escape-html="false"` without any mess