fix legend titles, units, total plots

[orichters]

all images have left: old and right: new

• if all data is from the same model, state that in the legend title and shorten the line description.

• if all data is from the same scenario, state that in the legend title and shorten the line description.

• fix that the correct plot where to add the total is not found by specifying the identifier in showAreaAndBarPlots and passing that the scenario column before plotting the total. Fixes https://github.com/pik-piam/mip/issues/64

• fix strange coloring where multiple models had the same color

• add some simple tests for mipArea and mipLineHistorical
• fix size warning ggplot2 was complaining about and replacing by linewidth
• further harmonize parantheses around units
• add color.dim.name to further functions so it can be specified from outside (particularly piamInterfaces::plotIntercomparison. Will fix https://github.com/pik-piam/mip/issues/67

Here you can find further files old vs. new so you can see I have not broken compareScenarios2 etc: /p/tmp/oliverr/output/