Add additional statistics to the analysis of simulation output

[0liver0815]

Add median MTD and CV to simulation output, see issue #94

[0liver0815]

The calculation is done as follows:

1. After the final simulation run (stop criteria is hit), the dose that corresponds to the target is derived for each sample, .
2. In case that the target is an interval, the mean of the interval is used as target.
3. The median of the doses and the CV are derived and written to the simulation output.
4. In the summary method, the median of the medians and the mean of the CV over all simulated studies is derived.