Add function to create data summary

[dweindl]

For large measurement tables it would be great to have some functionality to generate some kind of report (graphical and/or tabular) showing, e.g.:

• number of conditions
• number of datapoints
• number of observables
• number of parameters (#estimated / #output parameter / ...)
• data points per condition
• data points per observable

[dweindl]

Closing. Was sufficiently addressed in #141.