Allow customizing all subobjects within any plot

[v0dro]

Currently many of the plots require that the user specify various options during the time of creating the plot which help in changing the nature of the plot. However, this limits customizability since the current design does not allow directly accessing elements inside a given plot (for example the boxes in a box plot).

This issue will require some redesign of the internals such that extensive customization of each element within the plot can be permitted by the user. Essentially, the current scheme of process_data -> make new objects -> draw those objects should change to make new empty objects -> process data -> populate empty objects with data -> draw those objects.