Adjusted margin for markdown list in tast-text. 

Closes #2721

When putting a `+` at the beginning of the task name, it gets translated to markdown, as expected, but since that turns into an `<li>` with default styling, the margin is all wonky.

## Before

![screen shot 2014-12-05 at 5 16 50 pm](https://cloud.githubusercontent.com/assets/2916945/5324649/f7846d84-7ca2-11e4-89d1-aabd5b1911d3.png)

![screen shot 2014-12-05 at 5 17 03 pm](https://cloud.githubusercontent.com/assets/2916945/5324651/fd81097c-7ca2-11e4-8c71-acfc07d09427.png)


## After

![screen shot 2014-12-05 at 5 18 33 pm](https://cloud.githubusercontent.com/assets/2916945/5324654/031abb4e-7ca3-11e4-939a-0f7bb82a6d9a.png)

![screen shot 2014-12-05 at 5 18 51 pm](https://cloud.githubusercontent.com/assets/2916945/5324655/0566e12a-7ca3-11e4-8060-16adc4207c68.png)


I'm being very specific here, because typing `+ + foo` results in a nested list, but it's not suppose to appear that way, so if the extra margin is on both, it creats a double dot:

![screen shot 2014-12-05 at 5 23 09 pm](https://cloud.githubusercontent.com/assets/2916945/5324700/669b316c-7ca3-11e4-8d5b-fda6de35802e.png)