ORKScaleSliderView: homogenize text choice slider constraints
ORKScaleSliderView: homogenize text choice slider constraints

Also, related to text choice slider:
 - Move label-creating code to init.
 - Do not create needless views on init.
 - Other small improvements.

jeremiahyan/ResearchKit,YuanZhu-apple/ResearchKit,DrGo/ResearchKit,jeremiahyan/ResearchKit,umerkhan-apple/ResearchKit,oliverschaefer/ResearchKit,boland25/ResearchKit,weijentu/ResearchKit,YuanZhu-apple/ResearchKit,mluedke2/ResearchKit,md0u80c9/ResearchKit,mluedke2/ResearchKit,KaiCode2/ResearchKit,boland25/ResearchKit,allen7wang/ResearchKit,QuintilesRK/ResearchKit,oliverschaefer/ResearchKit,jarrelscy/ResearchKit,danoli3/ResearchKit,cornelltech/ResearchKit,chb/ResearchKit,allen7wang/ResearchKit,weijentu/ResearchKit,DrGo/ResearchKit,jarrelscy/ResearchKit,danoli3/ResearchKit,oliverschaefer/ResearchKit,mluedke2/ResearchKit,boland25/ResearchKit,chb/ResearchKit,QuintilesRK/ResearchKit,shazino/ResearchKit,shazino/ResearchKit,DrGo/ResearchKit,weijentu/ResearchKit,umerkhan-apple/ResearchKit,jimmyti/ResearchKit,QuintilesRK/ResearchKit,KaiCode2/ResearchKit,KaiCode2/ResearchKit,cornelltech/ResearchKit,oliverschaefer/ResearchKit,jimmyti/ResearchKit,danoli3/ResearchKit,md0u80c9/ResearchKit,YuanZhu-apple/ResearchKit,cornelltech/ResearchKit,shazino/ResearchKit,jimmyti/ResearchKit,md0u80c9/ResearchKit,boland25/ResearchKit,weijentu/ResearchKit,allen7wang/ResearchKit,chb/ResearchKit,jarrelscy/ResearchKit,YuanZhu-apple/ResearchKit,jeremiahyan/ResearchKit,umerkhan-apple/ResearchKit,md0u80c9/ResearchKit,chb/ResearchKit