Add tree annotator settings to output as comments

It would be helpful if treeannotator logged the settings it used into the generated tree file (I'm dealing with a MCC tree that I need to describe but don't have info on e.g. burn-in, etc). Could be added as a nexus comment into the output:

```
[tree generated from file xx.trees using settings -height=CA -burnin=0 -topology=CCD0]
```