Support aux data in from_matched()

[jsmariegaard]

We would like to support aux data upon creating a Comparer with the from_matched() method.

A number of things have been changed in this PR. The most important are:

• from_matched() now has a aux_items argument
• from_matched() calls the Comparer class method from_matched_data() instead of creating
• from_matched() can now also take a dfs0 or a mikeio.Dataset in which case the quantity will be taken from the ItemInfo of the observation
• Comparer.sel() method now also filteres raw_data in time as it was very confusing to do cmp.sel(time="2019-01").plot.timeseries() and then get a plot also outside this time range
• Comparer now got a quantity property instead of an attribute avoid potential mis-alignment with info in Dataset
• Comparer variable_name renamed to quantity_name - next step is to use quantity.name instead
• A new notebook with examples have been added
• New tests

Things to consider:

• What should the default aux_items be? None? All in the input which is neither obs nor model?
• x, y columns are not yet supported in from_matched() but they could
• What default name should we give the Comparer? Or should we create a name argument in from_matched()