Shifu 0.2.7 Sampling Function Improvement

1. Posson Distribution Sampling for Bagging With Replacement Training Set baggingWithReplacement=true (default in Shifu 0.2.7) in training configuration. https://github.com/ShifuML/shifu/issues/93

2. Up Sampling Support In some cases if small ratio for positive records, up sampling for positive records are needed to train a more stable model. Look at https://github.com/ShifuML/shifu/issues/140 for details. Down sampling is already supported in norm#sampleNegtiveOnly and norm#sampleRatio.