Using a unique function to save both MultiCellDS data and intracellular data

[vincent-noel]

This comes as an effort to make the main.cpp of PhysiBoSS (and ultimately intracellular) models standard. As of now, the only difference is that after saving the MultiCellDS data, I'm also saving a CSV PhysiBoSS state file. And if other intracellular models wants to save state, they have to do the same.

The idea here is to have a wrapper function to include MultiCellDS and intracellular data save, that I called save_PhysiCell_Timepoint and stored in PhysiCell_various_outputs.

There will have no impact on the rest of PhysiCell, since in this PR only PhysiBoSS Cell Lines example is using this wrapper. But ultimately, it would be nice if all projects would use it, so that we get a standard main.cpp file.

There is no hurry for this, I just wanted to code it to see what it would look like, and have your opinion about this.