Fix sumstat issue

[xueweic]

1. add sumstat unit test
2. fix a bug for sumstat version without sample size
3. add a maximum iterations constraint for each outcome (M_single_outcome = 200, indicating the maximum iterations for each outcome is 200). This will solve the issue once sumstat and LD are mismatch, ColocBoost will stuck at the post-inference step, since gradient boosting update will stuck at the mismatch outcome.