Add an example on scenario selection for multi-scenario MORDM

[quaquel]

epa1361_ open contains an assignment on scenario selection for multi-scenario MORDM. This would be a sound basis for making an example, but then tie it to the systematic selection presented in Eker and Kwakkel (2018).

[EwoutH]

Link to that assignment, for reference: assignment 9 - multi-scenario MORDM.ipynb