Fixed issues with invalid cell layout

This small change fixes an issue with multi value section having invalid layout on iPad when a new row is added. 

Form table view cells use auto layout for laying out subviews, however the call after cell configuration used old 

'''
setNeedsLayout
'''

call to inform the cell that it should update its layout. This was changed to 

'''
setNeedsUpdateConstraints
'''

Example image how it looked before the fix: 

![screen shot 2014-04-22 at 5 51 04 pm](https://cloud.githubusercontent.com/assets/968513/2767884/46e25dfa-ca3d-11e3-8db8-1523ccb02a16.png)