Adjusting the intensity model in the simulation function

[yujing24]

1. Input for the simulation function: Baseline outcome value; fitted intensity model and the fitted outcome model (single index model)
2. Refer to the Web Appendix C: Simulation study in the "Semi-Parametric Sensitivity Analysis for Trials with Irregular and Informative Assessment Times"
3. Need to check the process of generating the next assessment time. In the original algorithm, there is an accept/reject process. (Check whether need to use the baseline intensities.)
4. For the outcome generation process, need to change it for the single index model version.