Reworking Retry

+ Moved retry.py into client.py
  + Changed from generator to simpler function
+ Changed lock time on cache to 10 seconds
+ Added some print '\n' statements for compatibility with RJSONIO library in R client
Accommodate API change from PLFM-2091

Changed addEvaluationParticipant to joinEvaluation.
Programmatically joining an Evaluation is now sort of convoluted.