Switched SUUpdateAlert.xib to AutoLayout

Problems: 

* Multiline text field doesn't expand to contain all lines of text: ![screen shot 2014-06-28 at 15 40 38](https://cloud.githubusercontent.com/assets/72159/3421024/41fa1110-fed2-11e3-84cf-99d624649abe.png)

* Multiline text field has wrong width and alignment in Arabic: ![screen shot -- at](https://cloud.githubusercontent.com/assets/72159/3421026/687eeafe-fed2-11e3-8f4f-091a5e9ab722.png)