Storing display settings in Preferences.jl

[bkamins]

@nalimilan, @ronisbr, @pdeffebach - what would you say if we stored display settings for DataFrames.jl in Preferences.jl?

Now we use ENV, but it is a bit clumsy and not persistent. Additionally then we could allow users to set more preferences.

The downside is that display would be a bit less reproducible.