Wrap text for options in multiselect

Solution for #1764

Instead of adding margin to left and right of `.search-choice` I've added a padding to `.chosen-choices`.
So no more `max-width: 95%`


This:
![screen shot 2014-03-11 at 16 32 13](https://f.cloud.github.com/assets/351038/2387011/5db0a6b2-a932-11e3-802f-5fe429440d99.png)

Becomes:
![screen shot 2014-03-11 at 16 26 13](https://f.cloud.github.com/assets/351038/2386996/29ef321c-a932-11e3-8891-4cddac452995.png)