Shorten visualisation chapter

[lgatto]

I would like to suggest to shorten the visualisation chapter by cutting the parts that we seem to skip systematically, namely

• the hexbin example
• all the ggplot customisation

and replace the latter with a link to relevant material (a ggplot vignette or chapter of the ggplot2 book) and a link to a ggplot2 figure gallery (there was a question asking about this at the Heidelberg workshop).

Comments, suggestions?

@csoneson , what do you think?

[csoneson]

I agree with removing the hexbin example. The customisation I'm less sure of - maybe it's useful to keep as an optional part in the end if nothing else to be able to point to the figures as an illustration that the appearance can be adapted and modified (with a plot that is familiar to the learner)? I guess we also skipped the composition of multiple figures last time - maybe that's also a candidate for skipping/labeling as optional (it feels like more of a new concept than the customisation).