Use both label() and value() methods to get text

Hi,

I see that currently there's a ```UIElement``` type check before getting actual text : for ```UIButton``` method ```label()``` is used, for others - ```value()```. But in many cases ```label()``` method returns visible text for non-button elements too. Please see screenshot.

![2014-08-13_16h38_03](https://cloud.githubusercontent.com/assets/5451824/3906966/af0ce072-22f7-11e4-97f6-26c5b99d1f1b.png)

I suggest to check whether ```label()``` method returns non-null & non-empty value, if so then return ```label()```. In other cases let's return ```value()```.
it's just for completeness)