comment on the structure of legend dictionary
make the title of each legend from a variable name (not aes type)
update TODO: how to improve legends
hide borders around legends (like in R ggplot2)
remove colons before legend labels (like in R ggplot2)
allow string keys in size legend

=> __main__ test doesn't crash anymore
Merge branch 'feature/var-names-in-legends'
Merge branch 'feature/r-look-and-feel'