Modify model setup + Add Cox models

Model Change

• Add hierarchical enforcement to the bi-level selection by imposing a dependency to the non-linear components inclusion indicator prior

Implementation

• Add Cox Proportional hazard additive models via bacoxph and bamlasso(family="cox")
• Add model tuning functions via tune.bgam and cv.bgam
• Add variable selection function for bamlasso models via bamlasso_var_selection