give right name to pre-process step1 and step3

give right name to pre-process step1 and step3.  
   The step1 will do down-sample/padding(if need),  denoise(if on), scene change detect(if on), and it will produce the spatial picture list for encode.   
   The step3 will do VAA calculation,  background detection(if on), adaptive quant calculation(if on), picture complexity analyze(if rc on).   It is helper for the encoder mode decision algorithm.   So rename the step1 and step3 to BuildSpatialPicList and AnalyzeSpatialPic

Review:
https://rbcommons.com/s/OpenH264/r/86/