Some text field fixes

I changed mText = inText; to mText=Std.string(inText); in the set_text function in TextField. The parameter is declared as String, so it should be a string there, but apparently it is possible that the underlying javascript variable when the code gets executed is actually a number. This made the mText.split("\n"); call in RebuildText crash. I'm not 100% sure of the origin of this number variable in my app, but I think that some JSON parsing have something to do with it.

I also changed the centering of text in text fields, so it works in _my_ app at least.